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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
Ok first off motor is fresh and broke in forged 355 vortec heads cc503 cam eddy intake and streetfire dizzy. choke isn't hooked up yet but always fires one pump of peddle and first hot with key. Base timing is 11 or 12 have to check again. Here's the issue cold start to warm up wideband sees 13.5afr. Idling After its warm afr goes 17+ .i did have a gas tank vacuum issue that has been solved I have plenty of fuel going to the carb 5.5 psi any thoughts? Also pulled front number 2 plug pic included.
I will spray something around and see if it idles up but everything is new and the gaskets all of it. A friend is letting me borrow a carb to try and see if it changes anything .
The least messy way is probably with an unlit propane torch, if you have one. Otherwise brake cleaner, carb cleaner, etc will get it done.
Double check the carb itself, too. If you have any vacuum ports plugged, make sure the caps haven't cracked. Or even verify that the carb mounting gasket is good to go. I've had pieces of gasket get stuck before, causing it to lift off on one corner without realizing it.
I have ran 18.0 idle air fuel ratio many times, on decel it would go to 25.
When I put a new deal together I do not look at AFR.
I tune to make the car react like it should.
Nothing wrong with high Idle AFR.
I would drive it on flat ground and jet it until I would get lean surge.
I would them come up in jet size until the surge was gone , then come up another .001 or .002 in jet size to be on the safe side.
This has always gave me part throttle cruise in the 14.5 area when checked on a chassis dyno after tweaks were finished.
To tune for full throttle I would see how the shift recovery was.
If it nosed over on the shift you are lean.
If 1/2 throttle passing you get surge add some fuel with the primary metering rod thin end. and test.. You may need to add jet to the secondary.
I would like to see more initial timing especially with that cam.
Closer to 18 initial.
Tune it to make it run really well then look and see if the AFR falls in line.
Mine always do.
First time on a chassis dyno Abel Racing the owner asked if I tuned my carb with a wide band..I said NO.
He said it was spot on and would not change a thing.
If your intake has the spreadbore pattern, you should require the square metal adapter plate to seal at the base of the carb. Without it, it's really close to not sealing. Look at the imprint left in your base gasket to confirm.
Thanks for the input guys I checked for a leak couldn't find one will look in more detail this Friday. I was reading that having a overlap in the cam can cause some false readings on a wide band. So I will be road testing to see what cruise and wot afrs look like. And as far as the timing I can't go much more with out making a stop in the distributor to be able to run more initial timing. I will report back soon after I do more testing.
I think he was saying that if it's a square bore carb on a spread bore intake, that you need an adapter or you have the potential of leaks from the base of the carb, among other things.
I think he was saying that if it's a square bore carb on a spread bore intake, that you need an adapter or you have the potential of leaks from the base of the carb, among other things.
Usually, soot indicates a rich condition or excessive idling. It can also mean weak spark, etc. I'd pull a couple of other plugs to see what they look like, too.
Ignore the AFR meter for a minute...how is the car running? If it is running okay, the. It is okay. And, as mentioned above, more initial advance would be better. You have vacuum a Vance hooked up?
What is your fuel pump setup? Are you running the stock efi pump or is your block old school with a mechanical pump? If you have the stock efi pump supplying the carb with a regulator and you disconnected the emmissions/ computer then there is your problem. I had the same issue few years back. What i did was make my own wiring harness for the fuel pump to a hot switch and it solved the problem. The computer controls the pump via voltage so you might see good fuel pressure at idle on initial startup but after a few minutes the voltage to the pump will drop causing you to run lean. All depends what setup you have for a fuel pump. My .02
Running a fuel pick up tube in the tank no electric pump. Just a block pump. I had a issue with the tank vacuuming so it would slowly cut off the flow but now I have that issue fixed I'm getting plenty of fuel.
Last night I re timed the car it was at 12 initial. Now it's at 18 degrees but I have to put a stop on the advance somehow because I'm getting over 35 degrees all in before 2500rpm and I kinda bounces around. On a side note where could I buy a distributor that is set up for my build .
Z - bouncing around sounds like springs are weak in distributor. Are you sure you are hooked to a ported vacuum on carb? GM dizzy wants zero vacuum at idle. 2500 all in would indicate either springs, advance plates, or adjustable dizzy out of wack. The sbc I have raced/used/built are typically good with 35-38 advance and love a bit more advance at start up. Most gm dizzys have about 20 degrees built in. Is the street fire vacuum adjustable and did you have this set up on a Dyno? More advance typically leans out afr numbers. Hope this helps... byron
Z - bouncing around sounds like springs are weak in distributor. Are you sure you are hooked to a ported vacuum on carb? GM dizzy wants zero vacuum at idle. 2500 all in would indicate either springs, advance plates, or adjustable dizzy out of wack. The sbc I have raced/used/built are typically good with 35-38 advance and love a bit more advance at start up. Most gm dizzys have about 20 degrees built in. Is the street fire vacuum adjustable and did you have this set up on a Dyno? More advance typically leans out afr numbers. Hope this helps... byron
I actully had worse bouncing with the light springs these are the heavest springs i have in my kit. Vac advance unhooked when I re timed. Vac advance is set to least level anyways I think 8 degrees. No car is sitting im my garage. Im ready to burn this thing.
Z - I am confused. If you are on a ported vacuum there should zero vacuum at idle. Only when you give a bit of fuel should the vacuum come on. 10-12 with zero vacuum + 20 degrees should put you in the ball park. Curious, what is your converter? Stock? Personally, I would start at 15 degrees - get into the 34-38 degrees total. Back it down if it falls on its face - remember, more advance can cause lean conditions. Have you verified that the timing pointer is correct - you are actually @ 8 degrees? Only 28 degrees total? Get the timing first - then get the spark - all in @ 2500 is fine if you are running a loose converter. If your afr is good at idle - then the jets come into play. I make that statement with the anticipation that your carb is good. Byron
Z - I am confused. If you are on a ported vacuum there should zero vacuum at idle. Only when you give a bit of fuel should the vacuum come on. 10-12 with zero vacuum + 20 degrees should put you in the ball park. Curious, what is your converter? Stock? Personally, I would start at 15 degrees - get into the 34-38 degrees total. Back it down if it falls on its face - remember, more advance can cause lean conditions. Have you verified that the timing pointer is correct - you are actually @ 8 degrees? Only 28 degrees total? Get the timing first - then get the spark - all in @ 2500 is fine if you are running a loose converter. If your afr is good at idle - then the jets come into play. I make that statement with the anticipation that your carb is good. Byron
I'm currently set at 18 initial now idle seems a bit better as suggested . 8 degrees is how much I have the vac advance limited to with a stop plate. Car is a t56 swap so no converter. Car also is a vortec so I can't run more than 32-34 . Reason I asked about locking out the distributor instead is 2 guys I know that race locally run 602 crates (vortec motors) and they both run welded advance plates and run about 29 degrees to 32 degrees advance. Curious if I would be able to do something similar with out to many I'll effect s sorry if my posting is all over the place I'm just trying to get this thing running good enough to drive it and not worry about trashing my brand new motor that I spent alot of money building last year. Thanks.
Z - I am confused. If you are on a ported vacuum there should zero vacuum at idle. Only when you give a bit of fuel should the vacuum come on. 10-12 with zero vacuum + 20 degrees should put you in the ball park. Curious, what is your converter? Stock? Personally, I would start at 15 degrees - get into the 34-38 degrees total. Back it down if it falls on its face - remember, more advance can cause lean conditions. Have you verified that the timing pointer is correct - you are actually @ 8 degrees? Only 28 degrees total? Get the timing first - then get the spark - all in @ 2500 is fine if you are running a loose converter. If your afr is good at idle - then the jets come into play. I make that statement with the anticipation that your carb is good. Byron
also with anything over 14 degrees initial timing I will be over my desired all in timing with out Making a stop plate of some kind for my mechanical advance. And I have no way to gauge the right spot for exactly where I would need it another reason I was curious about locking it out.knowing my timing would never be more than the motor would like to have.
Ok well update before I lock out timing I decided to go 14 degrees initial. And against better judgment (no plates on car) took it out of the drivway and to the next street down turned around afr seemed to be between 12.5 and 14 until I idle once idling the afr goes high again. And rpms go to around 500 idle normally is around 800. It never stalls out tho. Not sure on what's there is for power as I didn't dare get after it last time lady called cops. But other than the weird drop in rpm seemed normal ish low rpm take off bucked a tiny bit but I was also trying to go real slo taking off with a stage 3 clutch and might have had something to.do with the profile of the cam .... thoughts? Might be good enough to have a friend tow it to somewhere we could drive it for a bit?
Ok well update before I lock out timing I decided to go 14 degrees initial. And against better judgment (no plates on car) took it out of the drivway and to the next street down turned around afr seemed to be between 12.5 and 14 until I idle once idling the afr goes high again. And rpms go to around 500 idle normally is around 800. It never stalls out tho. Not sure on what's there is for power as I didn't dare get after it last time lady called cops. But other than the weird drop in rpm seemed normal ish low rpm take off bucked a tiny bit but I was also trying to go real slo taking off with a stage 3 clutch and might have had something to.do with the profile of the cam .... thoughts? Might be good enough to have a friend tow it to somewhere we could drive it for a bit?
I think I figured it out! Car runs good cold once warmed runs like trash..... electric choke wasn't getting 12v+ power ..... so obviously from what it looks like choke is still closed cause no power to open the flap does this make sense? Also could have been seeing a false lean because the mixture was so rich. How did I miss something so simple.
Sounds like you found your problem.You may want to move your fuel filter so its not being heated by header pipe on #2 cylinder.Cant tell the distance from your picture ......but its right above the exhaust.
06-25-2017, 09:59 PM
