what rods/jets on non-cc q-jet on a medium 350
06-02-2006, 12:01 AM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
what rods/jets on non-cc q-jet on a medium 350
Just wondering what primary rod/jet combo guys are running on a mild/medium 350 ?
I've got a lot of tweaking to do, I just put in a new primary piston so it'll seat at idle.... I still don't really get any adjustment from my mixture screws, and i've got a harsh bog when punching it.... I think a kinked fuel line may be effecting this a bit...
anyway, if anyone has run a ~350HP 350CID with a non-cc q-jet, please give me a ballpark for primary settings. Thanks! (motor in sig)
I've got a lot of tweaking to do, I just put in a new primary piston so it'll seat at idle.... I still don't really get any adjustment from my mixture screws, and i've got a harsh bog when punching it.... I think a kinked fuel line may be effecting this a bit...
anyway, if anyone has run a ~350HP 350CID with a non-cc q-jet, please give me a ballpark for primary settings. Thanks! (motor in sig)
06-02-2006, 01:39 AM
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Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
68-73 primary jets, 48-50M rod primary, DA or DR secondary rods on a F and sometimes K hanger, 7/8 to 1 turn Air Valve windup
06-02-2006, 09:58 AM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
? That sounds extremely lean part throttle. Was that in your van?
So far i've got 72 jet, 43 rods I think. I'm not sure if i've got a lean/rich stumble, or if it's due to lack of fuel flow through the kinked hose, or a combination of many things...
So far i've got 72 jet, 43 rods I think. I'm not sure if i've got a lean/rich stumble, or if it's due to lack of fuel flow through the kinked hose, or a combination of many things...
06-02-2006, 10:31 AM
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It's pretty much impossible to guess at a rod/jet combo without knowing ALOT more about the carb.
In particular, the main air bleeds could be any size from about .025" up to about .100". The smaller the bleed, the greater the signal, and the smaller the jets will need to be. There are a few other things that affect the main system mixture too; but that's probably the single biggest one.
That ONE DIFFERENCE would result in a good .006" jet variation, from one carb to another. Maybe more. In other words, any number anybody gives you, could EASILY be that far off. Which is like half of the entire possible range of jet sizes.
Older carbs, like 7029202 (the all-time best Q-Jet core for small block use), have the very small air bleeds (brass inserts) and large main wells. Smogger carbs, like any 704xxxx or 1705xxxx number, will have large bleeds, maybe even no insert at all; and small main wells, sometimes not much bigger than .080". In other words, the well actually becomes a metering restriction. Those make terrible cores for a performance build-up. The ones out of trucks AND VANS make the absolute worst possible cores.
Then there's all the differences in idle circuits, which there's just a dizzying variety of idle air bleeds, restrictions at the tip of the idle tubes (brass tubes pressed into the carb body and terminating in a calibrated tip about 1½" below the top of the fuel bowl where you can't get to them), and other details. Again, the 70s & 80s smogger units, especially truck AND VAN and sedan carbs, are AWFUL to try to get to work with bigger cams. The idle passages simply are too small to flow enough fuel at the amount of signal (signal being manifold vacuum, in the case of the idle system) that's available. Fortunately the Q-Jet idle circuit is less important at cruise than some other carbs; but it can still be a real bear to get that part of it to ever work right. The CC Q-Jets are also very difficult to change the idle system significantly, and that's the usual reason that their mod capabilities get exceeded.
Best way to calibrate a Q-jet is to start with the mains. Disable the secondaries by removing the link, and tune the jets for best 1320' mph. Then tune the rods for something like best 50mph - 60mph acceleration with the vacuum held constant at 12". Then do whatever you have to do to get it to idle. Then tne the secondaries for max mph in the 1320; start with ½ turn of tension on the AV spring for a 350. With a 350, if you have to put more than ¾ turn of AV tension on it, the rods are too lean.
In particular, the main air bleeds could be any size from about .025" up to about .100". The smaller the bleed, the greater the signal, and the smaller the jets will need to be. There are a few other things that affect the main system mixture too; but that's probably the single biggest one.
That ONE DIFFERENCE would result in a good .006" jet variation, from one carb to another. Maybe more. In other words, any number anybody gives you, could EASILY be that far off. Which is like half of the entire possible range of jet sizes.
Older carbs, like 7029202 (the all-time best Q-Jet core for small block use), have the very small air bleeds (brass inserts) and large main wells. Smogger carbs, like any 704xxxx or 1705xxxx number, will have large bleeds, maybe even no insert at all; and small main wells, sometimes not much bigger than .080". In other words, the well actually becomes a metering restriction. Those make terrible cores for a performance build-up. The ones out of trucks AND VANS make the absolute worst possible cores.
Then there's all the differences in idle circuits, which there's just a dizzying variety of idle air bleeds, restrictions at the tip of the idle tubes (brass tubes pressed into the carb body and terminating in a calibrated tip about 1½" below the top of the fuel bowl where you can't get to them), and other details. Again, the 70s & 80s smogger units, especially truck AND VAN and sedan carbs, are AWFUL to try to get to work with bigger cams. The idle passages simply are too small to flow enough fuel at the amount of signal (signal being manifold vacuum, in the case of the idle system) that's available. Fortunately the Q-Jet idle circuit is less important at cruise than some other carbs; but it can still be a real bear to get that part of it to ever work right. The CC Q-Jets are also very difficult to change the idle system significantly, and that's the usual reason that their mod capabilities get exceeded.
Best way to calibrate a Q-jet is to start with the mains. Disable the secondaries by removing the link, and tune the jets for best 1320' mph. Then tune the rods for something like best 50mph - 60mph acceleration with the vacuum held constant at 12". Then do whatever you have to do to get it to idle. Then tne the secondaries for max mph in the 1320; start with ½ turn of tension on the AV spring for a 350. With a 350, if you have to put more than ¾ turn of AV tension on it, the rods are too lean.
06-02-2006, 11:32 AM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
hmm, thank you sofa. I've got plenty of info on this topic, a book, manuals by "Lars", Damon etc. I've heard all kinds of varying info on how to modify those air bleeds, grinding off the casting plugs, then drilling, drilling from the top etc..... So far mine are virgin.
I have drilled the throttle plates to keep it idling. 1 1/16" hole in each primary blade.
oh yea, it's a 17084xxx carb I believe. off an '84 cutlass sedan LG4.
It seems to idle pretty well, and off idle is ok, no noticeable bog. But leaning into it causes all kinds of bogs and stutters. I've got enough timing at idle to keep the primary blades shut enough to have a transition slot working.
That was my plan, to lock out secondaries, and go WOT (power piston spring to pull out my rods), and hence tune my jets. Now, should I do runs and check the plugs for mixture as well, or just purely compare speed? I was thinking of cleaning a spark plug, doing the run, marking time to go from x->x speed, then shutting it down right after the run, and checking the plug, so I know what direction to go in.
I was planning on doing a 4th gear, 40mph-80mph run or something, to take away the variable of my shifting. sound do-able?
then finally, how do I test the rods? mainly, how do I keep constant vacuum? Punch the gas and it drops...? I have a max of 10" vacuum idling, so i've got a power piston spring in there now that'll come out at ~7". I used an old float bowl, and pressed in a vacuum tube into the base below the power piston, then hooked it up to my car while idling, then cupped my hands over the choke air horn to get it almost to die, then watch when the piston comes up. Not all that accurate, but better then what was in car at first .
I'm going to go down to the JY and grab more jets/rods, the few i'm missing, then go tuning. Thanks for the help so far!
I have drilled the throttle plates to keep it idling. 1 1/16" hole in each primary blade.
oh yea, it's a 17084xxx carb I believe. off an '84 cutlass sedan LG4.
It seems to idle pretty well, and off idle is ok, no noticeable bog. But leaning into it causes all kinds of bogs and stutters. I've got enough timing at idle to keep the primary blades shut enough to have a transition slot working.
That was my plan, to lock out secondaries, and go WOT (power piston spring to pull out my rods), and hence tune my jets. Now, should I do runs and check the plugs for mixture as well, or just purely compare speed? I was thinking of cleaning a spark plug, doing the run, marking time to go from x->x speed, then shutting it down right after the run, and checking the plug, so I know what direction to go in.
I was planning on doing a 4th gear, 40mph-80mph run or something, to take away the variable of my shifting. sound do-able?
then finally, how do I test the rods? mainly, how do I keep constant vacuum? Punch the gas and it drops...? I have a max of 10" vacuum idling, so i've got a power piston spring in there now that'll come out at ~7". I used an old float bowl, and pressed in a vacuum tube into the base below the power piston, then hooked it up to my car while idling, then cupped my hands over the choke air horn to get it almost to die, then watch when the piston comes up. Not all that accurate, but better then what was in car at first .
I'm going to go down to the JY and grab more jets/rods, the few i'm missing, then go tuning. Thanks for the help so far!
06-02-2006, 01:15 PM
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What you just said about the vacuum and the power piston, is yet another Q-Jet tuning issue that comes with too much cam.
What has happened is, you weakened the power piston spring enough that it stays down while idling; problem is, in order for the carb to go into power enrichment, now the vacuum has to drop below 7" or whatever when driving it too. I.e. you're cruising down the freeway, your vacuum is 15" or something, you want to speed up a mile or 2 an hour, you come to a hill; vacuum goes down, say to 9"; but you've got no power enrichment, so now you're probably 2 points or more leaner than you want to be, and the motor will surge and complain. You get one of those loooooonnnnnnnng flat spots that you only get out of by giving it LOTS of throttle, at which point it suddenly snaps out of it and takes off.... when the power piston finally comes up.
Hook your vacuum gauge up, and tape it to the windshield or mirror or something, and use the throttle to control it. When doing the constant-vacuum runs, you want it in high gear to load the motor as much as possible, so yeah, avoid shifting.
I use strictly the mph to test the mixture. To use the plugs, you'd have to put in new plugs, do a WOT run, shut it down RIGHT THEN AND THERE WITHOUT LETTING IT IDLE, and pull the plugs. Not practical in the real world.
Q-Jets aren't a whole lot of fun to try and calibrate, if the jets & rods and maybe main air bleeds don't get it done. All of the idle stuff in particular is EXTREMELY difficult to work on, and even more difficult to put back and start over if you go too far. They're a great carb, but lack some of the tuning "handles" that make tuning it possible.
You've got a very bad core to start out with. I'm not surprised you're havin gtrouble dialing it in. The number I gave is for a 69 Chevelle 350. If you can find one of those that isn't ate up with the various old-age diseases like throttle shaft wear and electrolysis in all the screw threads and all that usual stuff, you'll be amazed at how much difference it makes just to start out with the right core.
Doug Roe's book is THE one to get, BTW.
What has happened is, you weakened the power piston spring enough that it stays down while idling; problem is, in order for the carb to go into power enrichment, now the vacuum has to drop below 7" or whatever when driving it too. I.e. you're cruising down the freeway, your vacuum is 15" or something, you want to speed up a mile or 2 an hour, you come to a hill; vacuum goes down, say to 9"; but you've got no power enrichment, so now you're probably 2 points or more leaner than you want to be, and the motor will surge and complain. You get one of those loooooonnnnnnnng flat spots that you only get out of by giving it LOTS of throttle, at which point it suddenly snaps out of it and takes off.... when the power piston finally comes up.
Hook your vacuum gauge up, and tape it to the windshield or mirror or something, and use the throttle to control it. When doing the constant-vacuum runs, you want it in high gear to load the motor as much as possible, so yeah, avoid shifting.
I use strictly the mph to test the mixture. To use the plugs, you'd have to put in new plugs, do a WOT run, shut it down RIGHT THEN AND THERE WITHOUT LETTING IT IDLE, and pull the plugs. Not practical in the real world.
Q-Jets aren't a whole lot of fun to try and calibrate, if the jets & rods and maybe main air bleeds don't get it done. All of the idle stuff in particular is EXTREMELY difficult to work on, and even more difficult to put back and start over if you go too far. They're a great carb, but lack some of the tuning "handles" that make tuning it possible.
You've got a very bad core to start out with. I'm not surprised you're havin gtrouble dialing it in. The number I gave is for a 69 Chevelle 350. If you can find one of those that isn't ate up with the various old-age diseases like throttle shaft wear and electrolysis in all the screw threads and all that usual stuff, you'll be amazed at how much difference it makes just to start out with the right core.
Doug Roe's book is THE one to get, BTW.
06-02-2006, 01:44 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
yea, i've got that book by Roe, that's the one I meant. I think with all the modifications done, that are listed in that book, i'd be in the same neighborhood as a better core. I just wasn't sure how far i'd need to go on a relatively mild motor such as mine.
yea, a '69 chevelle carb will be like trying to find a ferrari in the JY I'd think. I'll keep my eyes peeled though.
hmm, good point with the power piston spring, a nice long bog, that sounds about right. I guess i'll cruise around with the vacuum gauge on my windshield, and do some experimenting... But in that situation you listed, what is the solution? A power piston spring that comes off *right* below idle? (like 1"?)
Or is there a way to boost my idle vacuum? fixing my drilled throttle plates, and enlarging the idle air bleeds?
I've got a lot of testing and tweaking to do here... Thanks for the tips!
yea, a '69 chevelle carb will be like trying to find a ferrari in the JY I'd think. I'll keep my eyes peeled though.
hmm, good point with the power piston spring, a nice long bog, that sounds about right. I guess i'll cruise around with the vacuum gauge on my windshield, and do some experimenting... But in that situation you listed, what is the solution? A power piston spring that comes off *right* below idle? (like 1"?)
Or is there a way to boost my idle vacuum? fixing my drilled throttle plates, and enlarging the idle air bleeds?
I've got a lot of testing and tweaking to do here... Thanks for the tips!
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06-02-2006, 05:57 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
anywhere that shows manifold vacuum. Probe all of your capped off vac tubes, all of the ones that show the same, highest reading at idle, you can use any of those.
06-03-2006, 07:25 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
ok, did a fair bit of tuning today.
locked out the secondaries, and did a few runs, no bog or stumble...? hmm, so I went and swapped from F hanger, DR rods, to N hanger, CV rods (later secondary enrichment). Seemed much better... Then I took off the secondary lockout
, and it still seemed good!
I have 9-10" vacuum at idle. It dips a bit when i'm easing into 1st year say. Usually down to ~7".
Cruising, it holds about 10". When I let off the gas, and the butterflies are shut (except for the drilled hole...), then i'm at 14-20", engine braking. But maintaining speed with throttle keeps me at idle vacuum. Tap the gas much, and it'll dip down. Tap it down 1/2 throttle or so and i'm at ~4" which would bring up my primary piston. Punch it to the floor and it'll hold at 1".
I didn't swap any rods or jets on the primary side, as I don't have a good rod selection yet. I do however think that my throttle response, and low end powerband could be much better, so I will try more tuning, once I get a few more primary rods.
locked out the secondaries, and did a few runs, no bog or stumble...? hmm, so I went and swapped from F hanger, DR rods, to N hanger, CV rods (later secondary enrichment). Seemed much better... Then I took off the secondary lockout
, and it still seemed good!I have 9-10" vacuum at idle. It dips a bit when i'm easing into 1st year say. Usually down to ~7".
Cruising, it holds about 10". When I let off the gas, and the butterflies are shut (except for the drilled hole...), then i'm at 14-20", engine braking. But maintaining speed with throttle keeps me at idle vacuum. Tap the gas much, and it'll dip down. Tap it down 1/2 throttle or so and i'm at ~4" which would bring up my primary piston. Punch it to the floor and it'll hold at 1".
I didn't swap any rods or jets on the primary side, as I don't have a good rod selection yet. I do however think that my throttle response, and low end powerband could be much better, so I will try more tuning, once I get a few more primary rods.
06-05-2006, 01:32 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
ok, did some more testing:
locked out secondaries, then tried locking down a suitable primary jet size:
4th gear, got it to 60km/hr (35mph?), ~1300RPM, then punched it, and timed it to 100km/hr (60mph) ~2400RPM.
I can't really tell if it's too rich or too lean, so I was bouncing all over the place with jets. I forgot my 5/8" wrench to check the plugs
Tried 72, 75 & 77. 77 I'm pretty sure was much too rich, I removed the accelerator pump linkage and it seemed to have more snap. All of them were roughly 7 seconds, more timing error I think. I swapped rods a bit, but my test should have negated the rods effect (all .026" power tip.) I tried 43k, 49... I have a weak selection of rods between 43&49 so...
They all felt very sluggish, not just no secondaries sluggish, but very lazy. I'm thinking this is due to being below the cams powerband? Perhaps also too rich? i'm thinking too rich jets, too lean with rods. Maybe i'll try a 73/41 or something? Or do this at a higher RPM? I think it should be much faster just on the primaries though.
Any more thoughts or suggestions?
locked out secondaries, then tried locking down a suitable primary jet size:
4th gear, got it to 60km/hr (35mph?), ~1300RPM, then punched it, and timed it to 100km/hr (60mph) ~2400RPM.
I can't really tell if it's too rich or too lean, so I was bouncing all over the place with jets. I forgot my 5/8" wrench to check the plugs
Tried 72, 75 & 77. 77 I'm pretty sure was much too rich, I removed the accelerator pump linkage and it seemed to have more snap. All of them were roughly 7 seconds, more timing error I think. I swapped rods a bit, but my test should have negated the rods effect (all .026" power tip.) I tried 43k, 49... I have a weak selection of rods between 43&49 so...
They all felt very sluggish, not just no secondaries sluggish, but very lazy. I'm thinking this is due to being below the cams powerband? Perhaps also too rich? i'm thinking too rich jets, too lean with rods. Maybe i'll try a 73/41 or something? Or do this at a higher RPM? I think it should be much faster just on the primaries though.
Any more thoughts or suggestions?
06-05-2006, 01:58 PM
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Car: 1993 Nissan 240sx
Engine: Turbo KA24DE
Transmission: 5 spd
Axle/Gears: 4.08 VLSD
I was just gonna suggest you play with the accelerator pump. You say it had more snap when it was off, so that means it's running rich at that instant, right?
06-05-2006, 02:11 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
I was searching the other night, and came upon your thread "first timer rebuilding a noncc qjet" and Damon recommended 76-78 jets, 42-46 rods or something, etc. I figured that meant 77 wasn't too rich for my setup, so I tried it....
well, when I jetted up to 77, it was real boggy. Felt lazy, like it was rich. According to something else I read, if you disconnect your acc pump, and it's better, that means you were running rich. I could go to the outer link on the acc pump, but I think lessening my pump shot from stock is going in the wrong direction. I think I may need to go to leaner jets....
oh, and I think i'll try opening up my idle bits, like the restrictor and air bleeds. Maybe close up the holes I drilled in the plates... That is, if I don't get any other differing opinions here...
where are the rest of the q-jet experts? Out driving?
well, when I jetted up to 77, it was real boggy. Felt lazy, like it was rich. According to something else I read, if you disconnect your acc pump, and it's better, that means you were running rich. I could go to the outer link on the acc pump, but I think lessening my pump shot from stock is going in the wrong direction. I think I may need to go to leaner jets....
oh, and I think i'll try opening up my idle bits, like the restrictor and air bleeds. Maybe close up the holes I drilled in the plates... That is, if I don't get any other differing opinions here...
where are the rest of the q-jet experts? Out driving?
06-06-2006, 10:42 AM
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Car: 1999 Pontiac T/A Firehawk
Engine: ***'s Engine
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I ended up with 73/43 jets/rods in my 84 when I was still running the ZZ4 in it. Anything more than 73 was too rich. Secondaries I believe I had a D hanger and DR rods. I frequently have to open the idle mixture feed screws to the non-smog size (0.093"? Check the Roe book) but don't have to do any other drilling on a 350 sized engine.
Primary jets affect everything.
Primary rods affect idle, off idle, and cruise.
Secondary rods/hangars affect WOT.
What I always do is this:
1. Disconnect secondary throttle linkage and tune WOT mix by selecting the correct jet size. Adjust the idle mix everytime you change jets. Once this is perfect, I usually try going down one Jet size for economy reasons. If you have a mostly strip car, don't bother.
2. Once the jet size is correct, tune the cruise and off idle system by selecting the appropriate rods and power piston spring. Make sure the power system isn't coming in too fast or too slow. Adjust the idle mix everytime you change rods.
3. Once THOSE are right, fine tune the idle mix. Now you should have a QJet that drives fine, but lacks "oomph" past about 3000 rpm.
4. Reconnect the secondary throttle linkage and re-tune the WOT mix by playing with the rods and hanger. I tend to set these up a little richer to compensate for my slightly leaner than optimal main jets.
Changing too much crap, or trying to tune the main jets with the secondaries enabled, is a recipe for frustration.
Primary jets affect everything.
Primary rods affect idle, off idle, and cruise.
Secondary rods/hangars affect WOT.
What I always do is this:
1. Disconnect secondary throttle linkage and tune WOT mix by selecting the correct jet size. Adjust the idle mix everytime you change jets. Once this is perfect, I usually try going down one Jet size for economy reasons. If you have a mostly strip car, don't bother.
2. Once the jet size is correct, tune the cruise and off idle system by selecting the appropriate rods and power piston spring. Make sure the power system isn't coming in too fast or too slow. Adjust the idle mix everytime you change rods.
3. Once THOSE are right, fine tune the idle mix. Now you should have a QJet that drives fine, but lacks "oomph" past about 3000 rpm.
4. Reconnect the secondary throttle linkage and re-tune the WOT mix by playing with the rods and hanger. I tend to set these up a little richer to compensate for my slightly leaner than optimal main jets.
Changing too much crap, or trying to tune the main jets with the secondaries enabled, is a recipe for frustration.
06-06-2006, 11:23 AM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
Thanks hawk.
When tuning the primary jets, do you go WOT from idle speed, and time the run, or from x RPM to y RPM? I'm just wondering if i'm below the cams powerband, and that's why i'm not seeing much difference in jet sizes.
Yea, i've got the idle mixture holes punched out to .092". I think i'll close up my primary throttle blade holes, then try it again. I think that's giving my a lugging at 1000-2000RPM when off throttle, or in very light throttle. Then if I can't keep it running, open up idle orifices and tubes.
Yea, i've got the Roe book with me here at work, i'll be doing some more light reading at lunch. Each read gives me more info.
Yea, after each jet change I re-adjusted my mixture screws, but it didn't really change anything... hmm, I think my drilled throttle butterflies may be effecting that.
When tuning the primary jets, do you go WOT from idle speed, and time the run, or from x RPM to y RPM? I'm just wondering if i'm below the cams powerband, and that's why i'm not seeing much difference in jet sizes.
Yea, i've got the idle mixture holes punched out to .092". I think i'll close up my primary throttle blade holes, then try it again. I think that's giving my a lugging at 1000-2000RPM when off throttle, or in very light throttle. Then if I can't keep it running, open up idle orifices and tubes.
Yea, i've got the Roe book with me here at work, i'll be doing some more light reading at lunch. Each read gives me more info.
Yea, after each jet change I re-adjusted my mixture screws, but it didn't really change anything... hmm, I think my drilled throttle butterflies may be effecting that.
06-08-2006, 10:40 AM
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Car: 1999 Pontiac T/A Firehawk
Engine: ***'s Engine
Transmission: T56
Originally Posted by Sonix
When tuning the primary jets, do you go WOT from idle speed, and time the run, or from x RPM to y RPM? I'm just wondering if i'm below the cams powerband, and that's why i'm not seeing much difference in jet sizes.
I think i'll close up my primary throttle blade holes, then try it again. I think that's giving my a lugging at 1000-2000RPM when off throttle, or in very light throttle. Then if I can't keep it running, open up idle orifices and tubes.
Yea, after each jet change I re-adjusted my mixture screws, but it didn't really change anything... hmm, I think my drilled throttle butterflies may be effecting that.
1) At idle, if you screw the mixture screws in all the way, will it stall?
2) How much of the transition slot is exposed when the car is idling? Get the idle speed set right and take the carb off the car; hold the throttle against the stop and look from underneath.
I just spent three weekends tuning my QJet on my Buick 455, so getting the idle speed, mixture, and holes sizes nailed down are all fresh in my mind. By the way, if you have ported vacuum at idle, the throttle is open too far. Ask me how I know
06-08-2006, 11:01 AM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
Thanks!
here, i'll show my sig to give motor info: (cam is 227/234, .521"/.535")
I was running with the holes in the blades, and ported vacuum. Manifold seemed to give me a hunting idle. I have 22* base timing, 14* mechanical, and 4* vacuum, on ported, due to the fact I put my vacuum lockout tab in too agressively. I'm going to get more vacuum advance, but I think if I use manifold vacuum, then i'd lower my base timing, then i'd need to lengthen my mechanical again.... groan! I think for now i'll just bump up my vacuum advance to ~12*, and keep it on ported.
The blades were closed just right, showed part of the transition slot, and it ran ok with the holes in the blades. I think that gave it an off idle stumble though. It seemed to chug and jerk at 1-2k RPM with light throttle. like coasting through a parking lot say... I'd almost have to ride the clutch.
I went ahead and plugged the holes in the blades last night. I haven't tried putting the mixture screws all the way in to stall the car yet though.
I'm at work, with my float bowl right now, i'm going to drill out my idle restrictor holes about 3-4 thou. I guess I don't have a long enough drill bit to do the idle tubes that are right next to the restrictor tubes, in the float bowl. I did however drill out the secondary air bleed tubes (the thinner tubes hanging down from the air valve plate), to .030" I think, from around .027" or so. I also put the 4 holes in the secondary fuel pickup tubes.
I do have .092" idle mixture holes.
ok, i'll do a WOT run from 2000RPM in 2nd, into the top of 3rd then. If I lift off the gas while shifting, i'll be putting more accelerator pump shot in, keep my foot on the gas while shifting then? That's why I was thinking stay in one gear...
I'll do those mods I listed tonight then try tuning the idle. I'm running 43k rods, 74 jets for now. If I can keep the idle ok, and off idle better, then i'll go ahead and try tuning the jets again tommorow or something.
here, i'll show my sig to give motor info: (cam is 227/234, .521"/.535")
I was running with the holes in the blades, and ported vacuum. Manifold seemed to give me a hunting idle. I have 22* base timing, 14* mechanical, and 4* vacuum, on ported, due to the fact I put my vacuum lockout tab in too agressively. I'm going to get more vacuum advance, but I think if I use manifold vacuum, then i'd lower my base timing, then i'd need to lengthen my mechanical again.... groan! I think for now i'll just bump up my vacuum advance to ~12*, and keep it on ported.
The blades were closed just right, showed part of the transition slot, and it ran ok with the holes in the blades. I think that gave it an off idle stumble though. It seemed to chug and jerk at 1-2k RPM with light throttle. like coasting through a parking lot say... I'd almost have to ride the clutch.
I went ahead and plugged the holes in the blades last night. I haven't tried putting the mixture screws all the way in to stall the car yet though.
I'm at work, with my float bowl right now, i'm going to drill out my idle restrictor holes about 3-4 thou. I guess I don't have a long enough drill bit to do the idle tubes that are right next to the restrictor tubes, in the float bowl. I did however drill out the secondary air bleed tubes (the thinner tubes hanging down from the air valve plate), to .030" I think, from around .027" or so. I also put the 4 holes in the secondary fuel pickup tubes.
I do have .092" idle mixture holes.
ok, i'll do a WOT run from 2000RPM in 2nd, into the top of 3rd then. If I lift off the gas while shifting, i'll be putting more accelerator pump shot in, keep my foot on the gas while shifting then? That's why I was thinking stay in one gear...
I'll do those mods I listed tonight then try tuning the idle. I'm running 43k rods, 74 jets for now. If I can keep the idle ok, and off idle better, then i'll go ahead and try tuning the jets again tommorow or something.
06-08-2006, 12:20 PM
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Car: 1999 Pontiac T/A Firehawk
Engine: ***'s Engine
Transmission: T56
You've got a bit bigger cam than I did (208/221, .474/.510), so maybe you do need the extra air. I dunno.
One of the problems I initially had on the Buick was that turning in the mixture screws didn't have much effect since I was running on the main system. There was a point, however, where I had no nozzle drip with the screws turned out, but if I turned them in it begin dripping instead of the engine stalling. As long as the throttle blade position looks good, you're ok. My suggestion would be to see if your carburetor is equipped with idle air bypass passages--some are, some aren't. I've found it to run smoother if you expand those, rather than drill holes in the throttle blades, because that way the air detours around the main system. I've got a few links to look at if you don't know what you're looking for:
http://camaro.dnsalias.com/Reference/Qjet%20IAB%201.jpg
http://camaro.dnsalias.com/Reference/Qjet%20IAB%202.jpg
On quite a few carbs I've seen, the passages in the air horn and float bowl are there, but the holes in the throttle body are not "drilled out".
Anyhow, an off idle stumble probably indicates that to much of the transition slot is exposed. I had exactly the same problem. I've found that the less of the transition slot that is showing, the better. I've had the best luck with the edge of the transition slot just BARELY showing below the throttle blades. This is also indicated by you saying the idle mixture screws don't have much effect--probably because it's getting a lot of its idle fuel from the transition slot. That's how it's always worked out on anything I've worked on. Some carbs show a lot of transition slot even with the blades compeltely closed, and I've found those to be much harder to get rid of off-idle problems on.
Your timing looks... strange for a car with such a large cam. What I ran on my car, which worked well, was 15* initial, 20* mechanical, and 15* manifold vacuum. Are you restricting the mechanical advance to get only 14*? Your total timing looks good--if you're happy with the mechanical & initial timing, I'd try and run it with 10* manifold advance. What I've always done to get the idle timing right is to disconnect & plug the vacuum advance, then turn the distributor until I get the best idle quality. At that point, measure the total amount of advance (my experience has been the average "hot" small block likes anywhere from 20* to 40* of idle timing). On my car it liked 30* best, so having already determined it wanted 15* initial to make the 35* total it was happy with, I set it up for 15* manifold advance. Always worked great.
As far as the WOT testing, I still can't tell if you have an automatic or a stick. Either way, it's best not to lift during the shift, as that allows the accelerator pump into the equation. Make sure to do it with the secondaries blocked off!
One of the problems I initially had on the Buick was that turning in the mixture screws didn't have much effect since I was running on the main system. There was a point, however, where I had no nozzle drip with the screws turned out, but if I turned them in it begin dripping instead of the engine stalling. As long as the throttle blade position looks good, you're ok. My suggestion would be to see if your carburetor is equipped with idle air bypass passages--some are, some aren't. I've found it to run smoother if you expand those, rather than drill holes in the throttle blades, because that way the air detours around the main system. I've got a few links to look at if you don't know what you're looking for:
http://camaro.dnsalias.com/Reference/Qjet%20IAB%201.jpg
http://camaro.dnsalias.com/Reference/Qjet%20IAB%202.jpg
On quite a few carbs I've seen, the passages in the air horn and float bowl are there, but the holes in the throttle body are not "drilled out".
Anyhow, an off idle stumble probably indicates that to much of the transition slot is exposed. I had exactly the same problem. I've found that the less of the transition slot that is showing, the better. I've had the best luck with the edge of the transition slot just BARELY showing below the throttle blades. This is also indicated by you saying the idle mixture screws don't have much effect--probably because it's getting a lot of its idle fuel from the transition slot. That's how it's always worked out on anything I've worked on. Some carbs show a lot of transition slot even with the blades compeltely closed, and I've found those to be much harder to get rid of off-idle problems on.
Your timing looks... strange for a car with such a large cam. What I ran on my car, which worked well, was 15* initial, 20* mechanical, and 15* manifold vacuum. Are you restricting the mechanical advance to get only 14*? Your total timing looks good--if you're happy with the mechanical & initial timing, I'd try and run it with 10* manifold advance. What I've always done to get the idle timing right is to disconnect & plug the vacuum advance, then turn the distributor until I get the best idle quality. At that point, measure the total amount of advance (my experience has been the average "hot" small block likes anywhere from 20* to 40* of idle timing). On my car it liked 30* best, so having already determined it wanted 15* initial to make the 35* total it was happy with, I set it up for 15* manifold advance. Always worked great.
As far as the WOT testing, I still can't tell if you have an automatic or a stick. Either way, it's best not to lift during the shift, as that allows the accelerator pump into the equation. Make sure to do it with the secondaries blocked off!
06-08-2006, 12:39 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
yea, I have a stick, 4 speed, the T10 trans.
I welded my mechanical advance travel shorter, since I needed more initial advance, to keep the motor running. Using manifold vacuum would have worked too, but it tended to hunt at idle, so I swapped to using ported vacuum.
Then again that hunting could have been the power piston not seating at idle (it wasn't), or the motor loading up due to richness, which I also think it was.
hmm, I don't remember if I have that channel in the air valve plate or not... I'll have to check that tonight...
ok, i'll drill out my channel restriction a tad, then put it together with the same rods and jets. I'll keep my primaries shut enough to block off most of the idle airflow, and hopefully my idle mixture screws can keep the motor running with 24* base timing.
I'll try this tonight and post after that.
Thanks!
I welded my mechanical advance travel shorter, since I needed more initial advance, to keep the motor running. Using manifold vacuum would have worked too, but it tended to hunt at idle, so I swapped to using ported vacuum.
Then again that hunting could have been the power piston not seating at idle (it wasn't), or the motor loading up due to richness, which I also think it was.
hmm, I don't remember if I have that channel in the air valve plate or not... I'll have to check that tonight...
ok, i'll drill out my channel restriction a tad, then put it together with the same rods and jets. I'll keep my primaries shut enough to block off most of the idle airflow, and hopefully my idle mixture screws can keep the motor running with 24* base timing.
I'll try this tonight and post after that.
Thanks!
06-08-2006, 09:38 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
ok, drilled out my idle channel restriction to .055". I put my F hanger and DR rods back on.
put the carb back together tonight, with no holes in the throttle plates. Got a bit more vacuum at idle, ~11" now. I drove it around, and boy did it feel LAZY! I'm thinking rich... I checked #1 plug, was totally black. I didn't bother cleaning it up. It seemed to slow it's idle down as I sat at a light, so i'm guessing it was loading up? I don't remember how far out the idle mixture screws were, 5 turns maybe.
so I turned the idle mixture screws in all the way, it wouldn't die, it didn't change it's pitch either... ? still got a 750RPM idle though.
so I turned them out 2 turns each, and took it for a spin. It changed it's tone.... Seemed to go when I hit the gas, for a brief second, then bogged like crazy, and wouldn't go anywhere. Checked a plug, white electrode tip.... hmmm.... Lean?
It's raining like crazy here, and i've got the open cowl, and I'm pretty sure i'm sucking in a lot of water. The motor sounded funny when I was coming back home as well, perhaps the sound of running lean?
I'm going to leave this until it quits raining, then take it out into the country, and lock out the secondaries, and tune it up right.
put the carb back together tonight, with no holes in the throttle plates. Got a bit more vacuum at idle, ~11" now. I drove it around, and boy did it feel LAZY! I'm thinking rich... I checked #1 plug, was totally black. I didn't bother cleaning it up. It seemed to slow it's idle down as I sat at a light, so i'm guessing it was loading up? I don't remember how far out the idle mixture screws were, 5 turns maybe.
so I turned the idle mixture screws in all the way, it wouldn't die, it didn't change it's pitch either... ? still got a 750RPM idle though.
so I turned them out 2 turns each, and took it for a spin. It changed it's tone.... Seemed to go when I hit the gas, for a brief second, then bogged like crazy, and wouldn't go anywhere. Checked a plug, white electrode tip.... hmmm.... Lean?
It's raining like crazy here, and i've got the open cowl, and I'm pretty sure i'm sucking in a lot of water. The motor sounded funny when I was coming back home as well, perhaps the sound of running lean?
I'm going to leave this until it quits raining, then take it out into the country, and lock out the secondaries, and tune it up right.
06-09-2006, 11:38 AM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
just wondering, how do I know what direction to go, leaner, or richer. So far i've got:
disconnect acc pump, better = was too rich before, worse = was too lean before
flick throttle, black smoke? = too rich
lazy overall feeling motor = too rich,
snap acceleration, then bog = too lean.
checking plugs
any other ways to tell? some of these are hard to tell.
Since I can't kill the motor by turning in my idle mixture screws all the way, that tells me to lean up the cruise system (jet-rod). Am I right here?
It also felt lean at WOT, so I think i'll go to a 72 main jet, and see if I have idle mixture screw adjustment then.
I don't want to put a hole in the piston by doing the wrong thing, and i'm kinda unsure of my abilities here.
Any thoughts or tips are much appreciated. I'll probably be doing this tonight. Thanks!
disconnect acc pump, better = was too rich before, worse = was too lean before
flick throttle, black smoke? = too rich
lazy overall feeling motor = too rich,
snap acceleration, then bog = too lean.
checking plugs
any other ways to tell? some of these are hard to tell.
Since I can't kill the motor by turning in my idle mixture screws all the way, that tells me to lean up the cruise system (jet-rod). Am I right here?
It also felt lean at WOT, so I think i'll go to a 72 main jet, and see if I have idle mixture screw adjustment then.
I don't want to put a hole in the piston by doing the wrong thing, and i'm kinda unsure of my abilities here.
Any thoughts or tips are much appreciated. I'll probably be doing this tonight. Thanks!
06-09-2006, 01:06 PM
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
Originally Posted by Sonix
Since I can't kill the motor by turning in my idle mixture screws all the way, that tells me to lean up the cruise system (jet-rod). Am I right here?
06-09-2006, 02:07 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
hmm, damn. So not being able to kill the car by closing off the idle mixture screws tells me....?
I'm thinking that means i'm off, too rich? I've got higher idle vacuum, so that's a promising note. But i've got an even worse bog in mid range / WOT, so... I'm not sure if I should go larger main jets or smaller?
Side note, I don't have any primary rods between 43-49. Edelbrock makes a 45 I think, but i'd like the full line up, just in case. Tearing apart every junkyard q-jet to get to the primary system is pretty time consuming, can anyone tell me certain carb #'s, ie 170xxxx, that might have the rods i'm looking for?
Thanks
I'm thinking that means i'm off, too rich? I've got higher idle vacuum, so that's a promising note. But i've got an even worse bog in mid range / WOT, so... I'm not sure if I should go larger main jets or smaller?
Side note, I don't have any primary rods between 43-49. Edelbrock makes a 45 I think, but i'd like the full line up, just in case. Tearing apart every junkyard q-jet to get to the primary system is pretty time consuming, can anyone tell me certain carb #'s, ie 170xxxx, that might have the rods i'm looking for?
Thanks
06-09-2006, 02:33 PM
#24
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
Not being able to kill the engine by closing the idle mixture screws tells you the throttle blades are open too much at idle.
06-09-2006, 02:45 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
damn, ok, didn't think of that. But my idle is barely 600RPM....
I'll try opening the mixture screws 3 turns maybe. Then closing my throttle blades, more, and find out how far I can close my throttle blades, until I can kill the motor by closing my mixture screws. Then with that throttle blade opening, i'll find my highest vacuum level with mixture screws.
06-09-2006, 06:23 PM
#26
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Think of all the time you could save by using a wideband O2 sensor in the exhaust pipe! Check out the Innovate one, works well for me!
There is a guy on ebay selling lots of new carb jets/rods, let me know if you don't find him I will look him up.
There is a guy on ebay selling lots of new carb jets/rods, let me know if you don't find him I will look him up.
06-09-2006, 07:19 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
hmm, I found
Ecarb / fuelcurve
swapsupply
One of those guys?
lots of jets, but no primary rods ...
yea, I'm hoping to avoid the wideband, I heard they're expensive, plus i'd have to drill my nice headers/y-pipe... then plug the hole later, or leave it in...
happen to know any carb #'s that would have 44-49 rods in them?
also, what do you think about my motor setup, 74 jets, go bigger or smaller or ...?
Ecarb / fuelcurve
swapsupply
One of those guys?
lots of jets, but no primary rods ...
yea, I'm hoping to avoid the wideband, I heard they're expensive, plus i'd have to drill my nice headers/y-pipe... then plug the hole later, or leave it in...
happen to know any carb #'s that would have 44-49 rods in them?
also, what do you think about my motor setup, 74 jets, go bigger or smaller or ...?
06-10-2006, 10:19 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
did the tuning last night.
tried down to 70 jets, 40 rods.
seemed smooth. I think it may be lean though. I went back to 72/43 later that night, and i've got that on now. I think it's rich at idle, 'cuz the car seems to shake more, and feels more rough... Went and did some 'spirited' driving.... Then my car started ticking...?
I'm thinking exhaust leak? I guess those are more frequent with lean (hotter) exhaust as well? I'm missing one header bolt 'cuz I couldn't fit it in next to the primary tube... bought new gaskets, will do that soon here.
alright, I think i've got a handle on how to change my fuel curve, my only problem left is how I know where to change it (leaner, or richer). I'm going to try 77/49. The only reason I don't do straight out acceleration runs, is that my shifting is a variable that i'm not terribly consistent with...
my final question to you all then, is there any other tips or tricks to finding out if i'm lean or rich? I'm having a tough time telling, as i'm pretty new to this.
tried down to 70 jets, 40 rods.
seemed smooth. I think it may be lean though. I went back to 72/43 later that night, and i've got that on now. I think it's rich at idle, 'cuz the car seems to shake more, and feels more rough... Went and did some 'spirited' driving.... Then my car started ticking...?
I'm thinking exhaust leak? I guess those are more frequent with lean (hotter) exhaust as well? I'm missing one header bolt
'cuz I couldn't fit it in next to the primary tube... bought new gaskets, will do that soon here.alright, I think i've got a handle on how to change my fuel curve, my only problem left is how I know where to change it (leaner, or richer). I'm going to try 77/49. The only reason I don't do straight out acceleration runs, is that my shifting is a variable that i'm not terribly consistent with...
my final question to you all then, is there any other tips or tricks to finding out if i'm lean or rich? I'm having a tough time telling, as i'm pretty new to this.
06-12-2006, 12:41 PM
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Car: 1999 Pontiac T/A Firehawk
Engine: ***'s Engine
Transmission: T56
As you've probably guessed, I don't usually hang out here on the weekends. So let me add my $0.03 (inflation, ya know)...
1st, if the car will idle with the mixture screws all the way in, 99 times out of 100 that means that the throttle blades are too far open. Seated mixture screws means that NO fuel is flowing through the idle system, so if it's running, it's getting fuel from somewhere else--either the transition slots or the main system. After getting my Buick set, it runs rough with one screw seated and then stalls about 1 turn before the other screw seats (I have them about 3 turns out).
In the other 1 time out 100, it's one of two problems. Either leaky well plugs (0.99 times out of 1 ), or mixture screws that don't seat all the way. I've only run into the latter once. If you want to check, remove one of the screws, take the spring off, and reinstall it, seating it as far as it will go. If it goes noticeably farther in, you need to correct it. I think this is caused by drilling the idle feed AND using the later, finer taper mixture screws. To fix, snip a coil or two off the spring and reinstall. I also ran into this on my Buick, so it's rather fresh in my mind.
2nd, idle speed. You say your idle is barely 600rpm. Not being able to stall the engine with the mixture screws, yet having a low idle, means the engine can't get enough air with the throttle closed. This means that you NEED some sort of air bypass; either the IAB passages I showed you earlier drilled, or the holes in the the throttle blades reopened. Be careful drilling either; I used a set of numbered drill bits since they give you a FINE range of adjustment.
Here's a procedure for you:
1. Find a target idle RPM (700? 800?)--don't worry too much about the mixture right now. Adjust the throttle opening until you get that RPM.
2. Remove the carb and inspect the throttle opening. I'll bet you find a decent amount of the transition slot exposed. Drill bypass holes (or overdrill existing holes).
3. Reinstall the carb and check the idle. It should be higher. Close the throttle blades until you get your target RPM back.
4. Attempt to stall the engine by screwing the mixture screws all the way in. If the engine stalls, you're probably good. If not, go back to step 2 and try again.
Eventually you'll get the holes the right size. If it makes you feel better, I did this procedure about 15 times on the Buick before I got it right. Each time i got a little closer. Once you're finished, it should stall when you screw the idle mixture screws in, and you should be able to lower the idle noticeably below your set-point by backing the throttle set screw all the way off. It's not necessary to be able to stall the engine by closing the throttle; mine drops down to a very unhappy 550rpm out-of-gear idle when I close it, which is well below my desired 850rpm idle speed.
Once you get THAT, you can adjust your idle mixture. Hook up a vacuum gauge and dink with it until you get the highest possible idle vacuum. Keep in mind adjusting the screws will likely change your idle speed (I'm sure you know this), so you'll need to reset it a few times.
I'd get the idle problems set before you start tackling the main fueling curve. You'll have all sorts of off-idle and cruise issues if you don't fix that first. BTW, the jets do affect the idle mixture some, so everytime you change them, you'll have to readjust.
1st, if the car will idle with the mixture screws all the way in, 99 times out of 100 that means that the throttle blades are too far open. Seated mixture screws means that NO fuel is flowing through the idle system, so if it's running, it's getting fuel from somewhere else--either the transition slots or the main system. After getting my Buick set, it runs rough with one screw seated and then stalls about 1 turn before the other screw seats (I have them about 3 turns out).
In the other 1 time out 100, it's one of two problems. Either leaky well plugs (0.99 times out of 1
), or mixture screws that don't seat all the way. I've only run into the latter once. If you want to check, remove one of the screws, take the spring off, and reinstall it, seating it as far as it will go. If it goes noticeably farther in, you need to correct it. I think this is caused by drilling the idle feed AND using the later, finer taper mixture screws. To fix, snip a coil or two off the spring and reinstall. I also ran into this on my Buick, so it's rather fresh in my mind.2nd, idle speed. You say your idle is barely 600rpm. Not being able to stall the engine with the mixture screws, yet having a low idle, means the engine can't get enough air with the throttle closed. This means that you NEED some sort of air bypass; either the IAB passages I showed you earlier drilled, or the holes in the the throttle blades reopened. Be careful drilling either; I used a set of numbered drill bits since they give you a FINE range of adjustment.
Here's a procedure for you:
1. Find a target idle RPM (700? 800?)--don't worry too much about the mixture right now. Adjust the throttle opening until you get that RPM.
2. Remove the carb and inspect the throttle opening. I'll bet you find a decent amount of the transition slot exposed. Drill bypass holes (or overdrill existing holes).
3. Reinstall the carb and check the idle. It should be higher. Close the throttle blades until you get your target RPM back.
4. Attempt to stall the engine by screwing the mixture screws all the way in. If the engine stalls, you're probably good. If not, go back to step 2 and try again.
Eventually you'll get the holes the right size. If it makes you feel better, I did this procedure about 15 times on the Buick before I got it right. Each time i got a little closer. Once you're finished, it should stall when you screw the idle mixture screws in, and you should be able to lower the idle noticeably below your set-point by backing the throttle set screw all the way off. It's not necessary to be able to stall the engine by closing the throttle; mine drops down to a very unhappy 550rpm out-of-gear idle when I close it, which is well below my desired 850rpm idle speed.
Once you get THAT, you can adjust your idle mixture. Hook up a vacuum gauge and dink with it until you get the highest possible idle vacuum. Keep in mind adjusting the screws will likely change your idle speed (I'm sure you know this), so you'll need to reset it a few times.
I'd get the idle problems set before you start tackling the main fueling curve. You'll have all sorts of off-idle and cruise issues if you don't fix that first. BTW, the jets do affect the idle mixture some, so everytime you change them, you'll have to readjust.
06-12-2006, 01:30 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
hmm, ok, fair enough. It's not a huge hassle to screw with that, so I might as well give'r.
I have kinda a not stable idle, seems to be at 800RPM, then i'll do a WOT blast, and come back, and it'll be lower. I'll triple check my float setting too. I'll go ahead and get a PERFECT idle then, and then go back to primary stuff. Right now i'm at 75 jets, 49 rods FYI.
I don't really have any noticeable bogs, but it seems low on power, and right after a throttle opening, letting the blades close quickly gives me a quick surge of power (like 1/2 second)... Not sure if that's in my mind, or if that's somehow related to the primary butterflies closing, instant high vacuum, pulls more fuel...??? (standard trans, maybe just lurching forward against the gears, i'm not sure.)
As you guys can tell, I don't exactly have any mentors around, that have been driving carbed cars for a while, and this is my first carbed car, and first standard car. Put about 1000kms on it since I bought it, so most of this is new to me.
I'm pretty sure my well plugs are good, cold starting is flawless, one pump of gas and it fires up, goes to 1700RPM, floats down to 1400RPM in about 3 seconds, then sits there until I blip the throttle, and comes down to 700RPM.
And finally, (i'm kinda ahead of myself here), as far as adjusting cruise, ie, primary metering rods, therefore cruise area: I guess a "surge" would mean too lean, and too rich would just feel lazy? I don't know what a surge feels like, we're talking a momentary speed up? Like lurching, or...? Also, testing for best cruise area, sofakingdom (and others) mentioned a best 60-80MPH run, with constant vacuum..... I'm just wondering how this is done? If I push down the throttle, my vacuum drops off, due to the blades being opened... so ....? We're talking just light enough throttle to keep the vacuum above xx value? Go for a smooth (yet slow) acceleration?
Thanks muchly!
I have kinda a not stable idle, seems to be at 800RPM, then i'll do a WOT blast, and come back, and it'll be lower. I'll triple check my float setting too. I'll go ahead and get a PERFECT idle then, and then go back to primary stuff. Right now i'm at 75 jets, 49 rods FYI.
I don't really have any noticeable bogs, but it seems low on power, and right after a throttle opening, letting the blades close quickly gives me a quick surge of power (like 1/2 second)... Not sure if that's in my mind, or if that's somehow related to the primary butterflies closing, instant high vacuum, pulls more fuel...??? (standard trans, maybe just lurching forward against the gears, i'm not sure.)
As you guys can tell, I don't exactly have any mentors around, that have been driving carbed cars for a while, and this is my first carbed car, and first standard car. Put about 1000kms on it since I bought it, so most of this is new to me.
I'm pretty sure my well plugs are good, cold starting is flawless, one pump of gas and it fires up, goes to 1700RPM, floats down to 1400RPM in about 3 seconds, then sits there until I blip the throttle, and comes down to 700RPM.
And finally, (i'm kinda ahead of myself here), as far as adjusting cruise, ie, primary metering rods, therefore cruise area: I guess a "surge" would mean too lean, and too rich would just feel lazy? I don't know what a surge feels like, we're talking a momentary speed up? Like lurching, or...? Also, testing for best cruise area, sofakingdom (and others) mentioned a best 60-80MPH run, with constant vacuum..... I'm just wondering how this is done? If I push down the throttle, my vacuum drops off, due to the blades being opened... so ....? We're talking just light enough throttle to keep the vacuum above xx value? Go for a smooth (yet slow) acceleration?
Thanks muchly!
06-15-2006, 05:30 PM
#31
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I sent a pm afew days ago did you receive it?
----------
Try sending a email to the swap supply guy on ebay for the rods, if you don't find them I can try the Delco parts guy here, I usually get them for about $10 a set, but it has been a while since I have tried buying them from him. Are you using the long or short rods?
----------
Try sending a email to the swap supply guy on ebay for the rods, if you don't find them I can try the Delco parts guy here, I usually get them for about $10 a set, but it has been a while since I have tried buying them from him. Are you using the long or short rods?
Last edited by Rebuildman; 06-15-2006 at 05:41 PM. Reason: Automerged Doublepost
06-15-2006, 05:44 PM
#32
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
Well, the reason i'm not too keen on the wideband, is the monsterous $$. I'm toying with the idea of a simplier O2 sensor however(ie, cheaper.). I'm hoping to avoid this though. I might just buy a few new plugs, and install them out in the boonies while i'm trying my WOT runs. **Would it work to use a slightly different heat range then what i've got in the motor now? I'm using R42T, but they're hard to find, could I use an R43xx just for the sake of reading plugs?**
I haven't had a chance to touch it for a bit, i'm doing my u-joints tonight. Then i'll probably try like hawk mentioned, and check the blade angle, and reset it. Then maybe re-drill the throttle blades.
I did enlarge the idle channel restriction, to .055", do you think i'd need to do the idle tubes as well?
Yes I got your PM, sorry I didn't respond,..(did I?) I was hoping to avoid doing the idle tubes. I was thinking I could just drill the throttle plates instead?
I'm using the '75 and later rods... I forget, would that be the longer ones then?
I think i'll make sure i've got the idle bang on, first, then go and retry my power runs on the main jets, and ignore the primary rods basically. I have a good selection of primary jets. So once i've got those figured out, i'll *somehow* figure out which primary rods I need, then try and source those (assuming I need between 43-49 rods...)
Thanks!
I haven't had a chance to touch it for a bit, i'm doing my u-joints tonight. Then i'll probably try like hawk mentioned, and check the blade angle, and reset it. Then maybe re-drill the throttle blades.
I did enlarge the idle channel restriction, to .055", do you think i'd need to do the idle tubes as well?
Yes I got your PM, sorry I didn't respond,..(did I?) I was hoping to avoid doing the idle tubes. I was thinking I could just drill the throttle plates instead?
I'm using the '75 and later rods... I forget, would that be the longer ones then?
I think i'll make sure i've got the idle bang on, first, then go and retry my power runs on the main jets, and ignore the primary rods basically. I have a good selection of primary jets. So once i've got those figured out, i'll *somehow* figure out which primary rods I need, then try and source those (assuming I need between 43-49 rods...)
Thanks!
06-16-2006, 09:39 AM
#33
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Idle tubes have a hole that is smaller than the .055 hole in the idle channel restriction, so the tubes will limit fuel flow.
Metering rods not only have a different size tip but they also have a different taper designated by a letter, 44M, 44K, ect. You are using a carb with the first three #'s 170?
Off subject abit but do you know Conrad Gass in your town?
Metering rods not only have a different size tip but they also have a different taper designated by a letter, 44M, 44K, ect. You are using a carb with the first three #'s 170?
Off subject abit but do you know Conrad Gass in your town?
06-16-2006, 10:04 AM
#34
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
Yea, I know about that part of the idle tubes, but one article I read (written by Damon) seemed to let on that just modifying the idle channel restriction seemed to help...
I suppose modifying it to be removeable, will at the very least give me the ability to modify it... Maybe i'll do that tommorow...
Yes, my carb is 170. Most of my rods in my collection are K style. I think I have a few "M" style as well. K has a dual taper, and M is single correct? (But both can be used on my 170 carb?) And the 70xxx rods are too short, and can't be used right?
Conrad Gass? Can't say I do, big city here though, is he into 3rd gens, or racing? Might run into him at the track sometime?
I suppose modifying it to be removeable, will at the very least give me the ability to modify it... Maybe i'll do that tommorow...
Yes, my carb is 170. Most of my rods in my collection are K style. I think I have a few "M" style as well. K has a dual taper, and M is single correct? (But both can be used on my 170 carb?) And the 70xxx rods are too short, and can't be used right?
Conrad Gass? Can't say I do, big city here though, is he into 3rd gens, or racing? Might run into him at the track sometime?
07-02-2006, 02:26 AM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
ok, didn't have a chance to touch the car, as I was camping. Main problem was that I needed to get parts from the JY, which meant waiting for a weekend to get there.
So, recently I:
-put in a new tranny mount
-figured that since I can smell gas at idle, and it's bogging at low RPM, it may be running right. I thought my power piston was coming off too early. Swapped to a different one, yesterday.
-put in some crappy 87 octane gas by mistake
Car is running like garbage. I'm pretty sure it was detonating with the poor fuel. I burned through that gas in 24 hrs, so I put 20 litres of 91 in. Still running funny, whole car seems to shake more. Idle speed is steady as before, vacuum level is same, but more motor vibration going into car. I'm going to check my PS header flange, it was dicey before, and check my tranny mount, in case I goofed that....
-swapped back to original power piston spring. I'm getting 12-13" vacuum (fluctuates perfectly between 12-13" at idle). 3 turns out on idle mixture screws, 1/16" holes in butterflies.
-I'm running R42T plugs, and tried putting in a RV17YC in #1, so that I could read the plug easily. The delco plugs are black oxide coated I think, so they're harder to read, the champions are silver in color, hence my reason for using those. I ran the plug for ~1 km, cruise, just to check my cruise mixture. Nothing on the plug. So I put it back in, and drove home, ~30kms. Now it sure looks rich alright. Most of the plug is black, the side closest to the ground strap is black, the porcelin is half black (side close to ground strap), and blackish white on the far side.
Hopefully this isn't total ramblings here, i'm pretty lost.
Game plan for tommorow:
-check for vibration sources.
-does anyone have a suggestion for a power piston operating value? ie, if i'm getting that vacuum level, what piston spring do I want?
-if I disco a vacuum line, my idle speed goes up, does that mean i'm rich, or is that totally normal?
any and all thoughts are helpful, i'll be tinkering tommorow and hopefully get somewhere...
So, recently I:
-put in a new tranny mount
-figured that since I can smell gas at idle, and it's bogging at low RPM, it may be running right. I thought my power piston was coming off too early. Swapped to a different one, yesterday.
-put in some crappy 87 octane gas by mistake
Car is running like garbage. I'm pretty sure it was detonating with the poor fuel. I burned through that gas in 24 hrs, so I put 20 litres of 91 in. Still running funny, whole car seems to shake more. Idle speed is steady as before, vacuum level is same, but more motor vibration going into car. I'm going to check my PS header flange, it was dicey before, and check my tranny mount, in case I goofed that....
-swapped back to original power piston spring. I'm getting 12-13" vacuum (fluctuates perfectly between 12-13" at idle). 3 turns out on idle mixture screws, 1/16" holes in butterflies.
-I'm running R42T plugs, and tried putting in a RV17YC in #1, so that I could read the plug easily. The delco plugs are black oxide coated I think, so they're harder to read, the champions are silver in color, hence my reason for using those. I ran the plug for ~1 km, cruise, just to check my cruise mixture. Nothing on the plug. So I put it back in, and drove home, ~30kms. Now it sure looks rich alright. Most of the plug is black, the side closest to the ground strap is black, the porcelin is half black (side close to ground strap), and blackish white on the far side.
Hopefully this isn't total ramblings here, i'm pretty lost.
Game plan for tommorow:
-check for vibration sources.
-does anyone have a suggestion for a power piston operating value? ie, if i'm getting that vacuum level, what piston spring do I want?
-if I disco a vacuum line, my idle speed goes up, does that mean i'm rich, or is that totally normal?
any and all thoughts are helpful, i'll be tinkering tommorow and hopefully get somewhere...
07-03-2006, 12:06 AM
#36
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
hmm. if I put the car into top gear, putting around town at 1200RPM or so, and mash the throttle, instead of the lazy acceleration I expected, it shakes and rattles. I'm not sure if it's the y-pipe hitting the oil pan, that's kinda what it sounds like... but it stumbles like crazy....??
main million dollar question though;
That would give me some direction to go by.... I've got holes in the butterflies, would that mean i'm probably pulling fuel from the mains during idle? Perhaps that would cause overrich at idle? (then again, holes in the butterflies i'd think would cause too much air...) 
I swapped from 73/43 jets/rods to 75/50
10% leaner at cruise, 6% richer at WOT on primaries now. I also loosened up the AV tension. Still runs cruddy. I'm going to keep the secondaries locked out, and dink around with the primaries still.
What do you guys think, keep leaning it out all around?
main million dollar question though;
-if I disco a vacuum line, my idle speed goes up, does that mean i'm rich, or is that totally normal?
I swapped from 73/43 jets/rods to 75/50
10% leaner at cruise, 6% richer at WOT on primaries now. I also loosened up the AV tension. Still runs cruddy. I'm going to keep the secondaries locked out, and dink around with the primaries still.
What do you guys think, keep leaning it out all around?
09-12-2006, 11:27 PM
#37
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
k, after wiping 4 pesky lobes off that cam, (227/233), I have a new one, compxe268, 224/230, with 1.6 rockers. Everything else the same.
I also got around to putting in an O2 sensor, a 3 wire one.
I have a bit of a leak at the O2 bung, would that throw off my readings? I got some exhaust cement, i'll put on tommorow, but right now I have:
1/16" holes in the primary butterflies
600RPM idle.
13-14" idle vacuum
73/43 rods
.032" high speed air bleed
.055" idle channel restriction
untouched idle tubes
.1-.3V at idle and decel - Very lean - cranked open the idle mixture screws, richened it up a bit, but made idle rough. This is one reason I think I can't trust the O2 sensor right now.
~.5V at cruise, slightly lean, but not bad
.85-.95V on the primary power circuit. Sounds good. I think it likes the 73 jets.
I'm not sure if I should even pay attention to those numbers now, since the exhaust leaks at the O2 sensor...
It has an off idle stumble, mid range surge/stumble, stumble when on secondaries for a few seconds, but pulls well once well into the secondaries, until 5000RPM, then seems to hit a wall.
oh yea, I also replaced a plug wire that was arcing to the header pipes... no change in running...
I'm not sure if I should look at ignition or carb settings now.
I also got around to putting in an O2 sensor, a 3 wire one.
I have a bit of a leak at the O2 bung, would that throw off my readings? I got some exhaust cement, i'll put on tommorow, but right now I have:
1/16" holes in the primary butterflies
600RPM idle.
13-14" idle vacuum
73/43 rods
.032" high speed air bleed
.055" idle channel restriction
untouched idle tubes
.1-.3V at idle and decel - Very lean - cranked open the idle mixture screws, richened it up a bit, but made idle rough. This is one reason I think I can't trust the O2 sensor right now.
~.5V at cruise, slightly lean, but not bad
.85-.95V on the primary power circuit. Sounds good. I think it likes the 73 jets.
I'm not sure if I should even pay attention to those numbers now, since the exhaust leaks at the O2 sensor...
It has an off idle stumble, mid range surge/stumble, stumble when on secondaries for a few seconds, but pulls well once well into the secondaries, until 5000RPM, then seems to hit a wall.
oh yea, I also replaced a plug wire that was arcing to the header pipes... no change in running...
I'm not sure if I should look at ignition or carb settings now.
09-13-2006, 12:54 AM
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Car: 86 Z-28
Engine: 355 small block XR276HR roller cam
Transmission: TCI built 700r4 2000 lockup stall
Axle/Gears: moser axels auburn posi 3:73 gears
wow kinda going through something real similar with tuning issues here although im using the edelbrock thunder carb wish i could help. reading threw the thread i noticed something that jumped out at me, you wiped out four cam lobes ? how does this happen seems lile i hear of it quite abit. goodluck with your tune
09-13-2006, 08:35 AM
#39
Member
Cam lope damage usually occurs at break in. The oil companies have been re- formulating the oil and changing the additives to clean up emissions and it causes problems with the cam break in process. Also there was a real problem with lifters a few years back because the company that made them here in the U.S. went out of business and the off shore replacements were not as good. I believe Comp Cams is the place to buy the good ones now, could be some others, but them for sure. Also try using diesel oil in the motor for the first couple thousand miles, it has the additives needed for the break in. Also use the additive from the cam company mixed in.
The reason for holes in the primary throttle blades is because without them you can not get the blades closed enough to run on the idle circuit. When properly set at idle with out the holes you should have a very small portion of the slot in the bore uncovered by the blades, the only way to see this is to get the car to idle at the desired speed, 800 rpm?, then take the carb off the car and see where the blades are in relation to the slots. If you have a lot of the slot uncovered you are using the main circuit fuel to run on and not the idle circuit so drilling holes in the blades allows you to close the blades further and cover up the slot. Is this what has happened on your carb? It is not a good practice to have a hole in the blades if you can avoid it.
Here are the specs on power piston springs:7037734 14/4" dk. red, 7032758 11/5", 7037305 10/6" plain, 7036019 8/4" orange, 7029922 7/3" blue, 7037851 6/3".
The larger # is the point of vacuum that the piston starts to open, the smaller # is full open. Orange is the most common and the one normally used to start with.
The O2 sensor you are using is only good for telling you when you are NOT at 14.7 AFR which is 450 mv so keep that in mind. Usually for performance applications richer than 14.7 works better.
Using a 1975 and newer carb with a # 170 should use primary metering rods that are .080 inch shorter than the older rods. If the rod is stamped with a B it is a double taper rod.
Hope this helps!
The reason for holes in the primary throttle blades is because without them you can not get the blades closed enough to run on the idle circuit. When properly set at idle with out the holes you should have a very small portion of the slot in the bore uncovered by the blades, the only way to see this is to get the car to idle at the desired speed, 800 rpm?, then take the carb off the car and see where the blades are in relation to the slots. If you have a lot of the slot uncovered you are using the main circuit fuel to run on and not the idle circuit so drilling holes in the blades allows you to close the blades further and cover up the slot. Is this what has happened on your carb? It is not a good practice to have a hole in the blades if you can avoid it.
Here are the specs on power piston springs:7037734 14/4" dk. red, 7032758 11/5", 7037305 10/6" plain, 7036019 8/4" orange, 7029922 7/3" blue, 7037851 6/3".
The larger # is the point of vacuum that the piston starts to open, the smaller # is full open. Orange is the most common and the one normally used to start with.
The O2 sensor you are using is only good for telling you when you are NOT at 14.7 AFR which is 450 mv so keep that in mind. Usually for performance applications richer than 14.7 works better.
Using a 1975 and newer carb with a # 170 should use primary metering rods that are .080 inch shorter than the older rods. If the rod is stamped with a B it is a double taper rod.
Hope this helps!
Last edited by Rebuildman; 09-13-2006 at 08:39 AM.
09-13-2006, 03:45 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
yep, not quite sure how I wiped out the lobes, did everything text book correct. Lunati says it may have been due to going to synthetic after only 1000km, I think perhaps all the false starts, etc etc.
Yes, I had to crank open the idle screws very far to get a reasonable idle, so I drilled the holes, but the blades are still open too far. I think with holes in the blades i'm on the main system as well, so it's not a great solution anyway. I opened up the mixture screw holes to 3/32". I can't seem to get it to idle well, idle speed is 600RPM now, with ~22* base timing.
I'm going to cement the O2 sensor burnthrough holes (from pisspoor welding), and see if that changes my readings. I am seeing lean except for during WOT on primaries. It's sluggish performance, low torque, until i'm onto the secondaries anyway, so i'm not sure what's up. I'll try to tackle one problem at a time though.
Yes, I had to crank open the idle screws very far to get a reasonable idle, so I drilled the holes, but the blades are still open too far. I think with holes in the blades i'm on the main system as well, so it's not a great solution anyway. I opened up the mixture screw holes to 3/32". I can't seem to get it to idle well, idle speed is 600RPM now, with ~22* base timing.
I'm going to cement the O2 sensor burnthrough holes (from pisspoor welding), and see if that changes my readings. I am seeing lean except for during WOT on primaries. It's sluggish performance, low torque, until i'm onto the secondaries anyway, so i'm not sure what's up. I'll try to tackle one problem at a time though.
09-13-2006, 08:18 PM
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Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73
ok, plugging the O2 sensor bung leak changed things drastically... It shows rich of stoich at idle, and at cruise now. I might try and put a slightly fatter rod in, but I don't have one so...
anyone have 44 or 45 rods they can sell me?
I'm going to try some more trials now, seems like when I punch it, it takes off ok, but it really "hits" after about 1 second. Powerband? acc shot too small? vac break slowly breaking? air valve tension? hmm eh?
anyone have 44 or 45 rods they can sell me?
I'm going to try some more trials now, seems like when I punch it, it takes off ok, but it really "hits" after about 1 second. Powerband? acc shot too small? vac break slowly breaking? air valve tension? hmm eh?
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