i just put a non-cc quadrajet on my firebird today. it had sat a little while (about 6 months) and was taken off a running vehicle. obviously, there are so many factors in tuning carbs that no two cars will be alike, but i figured i could at least plop it on there and get some OK mileage.

putting around town the car acts GREAT! far better than the other carbs i've had on there. i had an edelbrock 1406 on it initially, then a holley 650 double pumper, followed by a barry grant road demon 650 and now this quadrajet. the problem i'm having is the car works great around town, but when i drop the hammer, it breaks up. it breaks up between about 2800-3800rpms and then clears back up and you can really feel the car moving again. off idle response is crisp, but it struggles up top. i'm thinking a possible lean condition. but what are some of the things to look for with these things? i don't know what the carb was originally intended for, other than maybe a mid 70's 350. the engine in my firebird is pretty much just that. it's the 260hp gm 350 crate motor. nothing special 8.5:1 and a baby camshaft.

as you can see, i don't really know where to begin with this carb, but i do know that i'm not giving up on it as i know that it can do well once tuned properly. if anyone has any insight or links to good reading material, that would be GREATLY appreciated

 

Sounds like your basic AV tension/rods/hangers tuning. Most factory q-jet rods are pretty lean.

 

Yep, sounds about right. Check what letter is stamped on the hanger, (K, F, etc) and pull the hanger (T8 screwdriver bit needed) and see what letters are stamped on the secondary rods. ie they might be DD, or AK, or...

Then adjust the secondary tension using a small flat blade and the right size allen key. I'm guessing about a 3/16" wide flat blade, and 1/8" allen key or so.
https://www.thirdgen.org/quadrajet

 

can ya'll post some pics of what you're talking about? i don't even know what half that stuff is...ok, just checked. the hanger has an "H" stamped on it. i have two other quadrajets, but they are CC style...one has a hanger with an "I" on it, the other is a "G". is this stuff interchangeable? if i don't have to buy anything....well...you guys know.

also, what would cause the car to diesel after i shut it off? the only changes i made was the carb swap. the timing is set at 15* initial

 

https://webdisk.ucalgary.ca/~jmknopp...ac%20port2.jpg
See the green linkage about where the purple arrow is?
Where it ends on the left, is the actuating rod for the secondary air valve. That's the two big flaps over the secondaries. Right about where that green linkage makes the 90* turn upwards, is where you put the flat blade screwdriver. You need to loosen the set screw (directly below it, allen key) before you can adjust the screwdriver part.

CC and non-cc share secondary hangers and rods. The closer to "A" the earlier it gets fuel. H should be fine for now.

Diesel - the idle screw is open too far, or the primaries or secondaries are hanging open a bit.

 

ok, i just went and adjusted the AV per the tech article and it's better but not quite there...there's still a flat spot between 2800 and about 3200 now...think that could be rods? do i have to change the jet sizes on these? (are there jets? lol!)

 

Hmm, I think I wrote a few really detailed posts about how these carbs work, and i'm sure Damon did too. I'm kinda busy at work, so I don't want to delve into it now, maybe on the weekend if you're still stuck.

They use jets AND rods, (in case you weren't joking and have no idea what's inside this carb...). Each part does a very specific function, and doesn't really overlap. That's what makes the carb beautiful, you can tune out anything.
Here's my webspace, I have 3 .doc files at the top about tuning q-jets.
https://webdisk.ucalgary.ca/~jmknopp/public_html/
Give those a read. The flat spot - does it feel too rich or too lean? Is this under heavy load/pedal or moderate?

 

the Q-jets are alot like the edelbrock that was on it. I have some stuff for that carb if you go back to it, that edelbrock is a good carb for gas mileage

 

so far, the edlebrock had the worst mileage of all the carbs and that was with me TRYING to get good gas mileage, all the others have had full throttle blasts for tuning's sake and have consistantly gotten better economy.

honestly, i need to make a WOT run again and shut it down and pull a plug, but i'm almost positive it's lean. it surges really badly. it's at anything over half throttle between 2600-3200 or so.

 

DR rods (if you can find them) and "B" hanger is a pretty hot ticket. I'm running DR rods on a "H" hanger. They made a big difference, even on the stock 305.

 

you gotta set layin' around? lol! could i get them from gm?

 

Not exactly. . .
Probably not.

Edelbrock has a few pieces http://www.edelbrock.com/automotive_...ss_q-jet.shtml

These guys have some as well http://www.carburetion.com/rodshang.asp

 

hmm....can you tell me what the carb has in it? or is there a list of whats supposed to be in it somewhere? 17085226 is the part number

 

From the Carbs Unlimited site:

"Rochester R-4 17085226 85-87 Chev/GMC/Truck BOP Grey Sol."

Doesn't say what rods/hanger, but those trucks and econo BOPs typically got pretty fat rods and high letter hanger.

Best bet is to take the hanger screw out, pull the rods, and look at what's stamped on them.

There is also a link in the "Please Read" sticky above about all of the secondary rods ever made, giving the particulars of their geometry. Remember the rods stick into holes in the bottom of the float bowl, so the bigger the diameter of the piece of rod sticking in the hole, the less fuel will flow. (I call them "holes" - they are precision-drilled, with no screw-in jet - hence, I don't call them "jets".)

 

so then my theory would probably be correct about the lean condition. cool. i'm gonna check out whats in it later tonight or tomorrow. i have two qjets at the house that likely have something else in them, i'll see if i can at least get the thing in the ball park.

should i take the carb off the engine to do the rod changes?

 

The only "difficult" part of the operation is getting the rods to hang straight and fit through the gasket and body holes when putting them back in while leaning over the fender. I suppose you could add "not losing the hanger screw" to that. Pulling the carb isn't necessary.

 

Maybe try locking your secondaries shut, and do a few WOT passes. Your primary system might be lean instead.
If the secondaries don't open at all, it'll only test the mixture on the primaries. It won't be very fast (be like having a 300cfm carb on there...) but it shouldn't have any lean/rich spikes at all. If that checks out, then start playing with rod/hanger combinations.

I had an extra set of DR rods around here, i'll see if I still have them.

 

got a trick to locking the secondaries closed? just do something so the AV flap doesn't open?

 

That would be the easiest way, although you could remove the link to the secondary throttle shaft - that way you'd know the secondaries are not having any effect.

 

There's a triangular linkage on the passenger side of the carb, which is connected to the choke. Basically when the choke is engaged (car is cold) it holds this tang on it, so that you can't go into secondaries.
Once the car warms up, this little triangular linkage falls down. I just use a 6" long piece of 18AWG wire (or string, etc) to hold up the *front* part of this linkage, so it is touching the other linkage, thereby blocking the use of the secondaries.

Unfortunately I don't have a good picture of this...

 

The piece you're talking about is disengaged by the fast idle cam. In order to engage it, you'll have to keep the fast idle cam weight up in the front.

https://www.thirdgen.org/forums/carb...e-rebuild.html

Figure 6C1-21. Item #34 is the secondary lock-out, #37 is the fast idle cam/weight (easy to find, it's green - although, I hear it isn't easy being green. . .).

 

sorry guys i wasn't able to play with the carb today. i got totally engulfed in the other part of this projects...the body stuff. nothing is really rough on it, it just needed a new bumper cover, and two fenders. got that stuff squared around though i'm gonna build my new y-pipe tomorrow, then i'll tackle the carb stuff when i'm all done with that.

 

ok, so i had a chance to pull the hangers and metering rods out to take a look see. here's what i found:


the far left set is on an I hanger and the rods say CH, this came out of a ccc-qjet that i had sitting in the shed

the middle set is on an H hanger and the rods don't have anything written on them, they came out of the non-cc-qjet i'm trying to get to work properly on the firebird. as you might can tell by the picture, one of the rods has a bent powertip...possible problem?

the set on the far right is another set of CH rods on a G hanger, also came out of a ccc-qjet.

which would you stab in there to get it going back down the road? this is what i have to work with for right now, i can buy more later, but for right this minute, this is all i have.

 

Hangers - Closer to "A" is 'faster'. It puts the rods higher up in the "jets". It means it will start to pull the rods up sooner. If you notice you're lean when coming into the secondaries, use a hanger that's closer to A. The differences are slight. G is probably best for you.
The bent power tip is pretty slight, i wouldn't worry too much about it. But
CH rods aren't bad, they are pretty common. Damon wrote up an atricle explaining which are which
, (which are leaner than others, etc). Try the CH ones. Adjust the tension on the air valve as well.

 

yeah, i did the air valve thing already, results were minimal. i slap the CH rods in with the G hanger and see what happens.

 

Try that, but I think the big results will come from when you find out exactly what is causing the surge/bog.
Lock out the secondaries and see if it does it. If it does, then you need to look at the primary system first.

 

ok. i think i need to spend some money and put a rebuild kit in it honestly. any friendly advice or tips to rebuilding it?

 

Well hold on, lock out the secondaries and rip around in it first. If it runs good and clean, then you don't need to rebuild it to play around with the secondaries.
If it does bog and stumble, at least you have a good starting point.
Then go by Napa (or whatever) and get a q-jet rebuild kit, A torx bit set (T15, T20, T8) and tear it down. But i'll give you a pile of tips when it comes to that, if need be.

 

ok, well, it's just that i already have the carb off the car cause i couldn't even get the damn thing to idle one night and so i just snatched it off and stuck my road demon back on it. i only payed $15 for the carb, so the fact that i was able to just plop it on and the car fired right up was just cool in itself. it had only sat for a couple of months between it being used last and me putting it on my motor, but i think it may have been long enough to possibly gunk the carb up.

i KNOW this carb is going to be the better carb once tuned properly, i just need to have the patience to work on it.

 

Ok, fair enough.
Niehoff is the common q-jet kit. they are universal. As you're tearing yours down, remember some parts. example - the gasket between the air horn (top plate) and float bowl (middle plate) will either have round bumps in the primary bores, or pointy bumps. Match it up to the new one.

Top plate - air horn
middle - float bowl
bottom - throttle body. (just to keep your terminology right)


-hitch #1 - the main throttle linkage actuates the accelerator pump (like a holley squirter eh?), and is connected via a rotating linkage on the top right side. You need to disconnect it to remove the air horn. There is a 3/32" roll pin holding this linkage in place. "They" say to use a small drill bit and hammer this INWARDS, until you can remove the linkage. I've seen some with the roll pin too long, so that even when the roll pin bottoms out on the air horn, I still can't remove the linkage. So I use a bent nail, to pry this roll pin OUTWARDS, until I can remove it and set it aside.

-Buy a carburetor adjusting tool from napa. $15 or so. Comes with a "double D" tool, that's the q-jet one. Need that to adjust the mixture screws.

-putting the air horn back on, with the power piston through the gasket correctly is tricky. Remember the power piston goes above the gasket. Make a note when you first remove the air horn. The lean stop for the power piston is a pretty important part. Don't remove it at all, IMHO. Or if you really feel the need to, then put it back to the same height. I use the depth measurement on my digital caliper. This may need adjustment, i'll give you a hint if need be later.

-Check all linkages for binding and whatnot. Wiggle everything (duh).

-Don't over tighten ANYTHING. Snug is lots.

- The carb kit will come with a diagram. Don't try to pry off the air horn, theres always a few screws we miss. HINT - two are in the primary bores. They are smaller than the others and are flat head vs pan head. Common snag for many here.

If I think of any other things i'll post up. Take lots of pictures if you can, it'll come in handy for someone here I guarantee.

 

ok guys, i picked up a rebuild kit for the carb today from work. i screwed up...i took lean stop out of the carb without measuring it's depth first...how do i go back to some sort of base line, and then how do i adjust it once assembled and back on the car? will i need to punch the plug out of the air horn that's covering it?

ugh...i'm an idiot, lol!

also, i have no idea how to set the float level on this thing....it's not really making sense to me how to do it...

 

Check the sticky at the top of the forum.

 

https://webdisk.ucalgary.ca/~jmknopp...owerPiston.doc

 

sonix, that was exactly what i needed, thank you so much sir. between the format and the diction, that paper almost seems like a disertation! lol! did you write that? either way, i managed to kind of do a hybrid of the quickie method and the precise method, so hopefully mine is quickly precise, lol! it's really cool to under stand how thing deals work, and i'm excited to get it back on the car now....

 

Yea, it's a very handy piece of paper. I can't take credit for it. It's another q-jet expert from the internet, Lars Grimsmud. I think he's a vette enthusiast, but he's written a number of little articles.
Glad it worked for you - well, here's hoping it worked...

 

Here's a pic of the choke controlled sec. lock-out linkage they were talking about.

Auggie

 

a lot of the stumbling as the secondaries are opening can be caused by the two small fuel discharge vents that are on the carb lid at the leading edge of the sec air door. In the carb body these vents are connected to a small fuel resivoir with down tubes. these tubes can get blocked and or fall out of the carb lid and sit in the fuel bowl cavity.
The small refill holes in this fuel cavity in the fuel bowl do get plugged up with dirt, corrosion and or carb fuel deposits as well.
especially if the carb has been sitting.
if this passive sec accelerator shooter system is not working right for any of the above reasons, the secondary air door/throttle response will always be a pain to dial in.
The air valve is controled by spring tension and the vacuum delay/choke pull off diaphram on the side of the carb. if the diaphram is fubared (common fault) the seconday transistion will never be smooth either. There is a small drilled orifice on the diapharm on the tube that the vacuum hose connects to that controls the vacuum pull off sec air door delay tming rate. Bigger orifice= faster door opening start point (less time delay)

You can experiment with the secondary metering rods by grinding a flat the edge of the stock rod to create your own custom progressive rod taper/fuel curve. if you screw up and grind a little too much (too rich), just get some more junk yard metering rods and start over.
The qjet has a very small fuel bowl and only 1 needle and seat fuel inlet. So fuel delivery volume capacity and fuel pressure att he carb are critical. The edelbrock .149" hi perf hi capacity needle and seat assembly allows more fuel flow. most stock Qjets have a .125" needle and seat. GM sells or used to sell a .135" big block Olds/Buick/Pontiac 455 HO/w-31/stage1 needle and seat. if the fuel bowl is draining low at high rpm this will help. I prefer the older, simpler pre 1975 4MV style Qjets.
I had one from a 1968 396-325 HP chevelle that always ran excellent, responed to tuning, easy to rebuild and made excellent power with good mileage on anything I put it on. Should have never sold it.

A anti desieliing throttle solenoid on the carb throttle linkage will eliminate the run on condition by completely closing the throttles off when you shut the ignition off. Cooler heat range spark plugs and higher (than 87) octane fuel help a lot too. If you do a lot of WOT running then the stock OEM spark plugs are too hot.
What intake manifold are your using?

CH 1350 292 1157 957 847 697 567 S 7045779 Your typical stock smogger Qjet rod

CV 1332 1291 1154 927 527 527 527 L 7045984 both a good step richer at WOT
AU 1345 1291 1154 927 527 527 527 L 7033655

DA 1333 1244 1075 847 577 440 440 M a good 2-3 steps richer @WOT Stock on edelbrock 850cfm Qjet.

CE 1347 1244 1075 847 547 410 410 M 7043771 much,much richer than stock. racing, open headers BB or built SB cold dense air.

CC 1347 1236 1129 1024 599 300 300 M 7042356 pig rich power tip. The richest edelbrock rod. supercharging/ turbo, radical open headers cold air race. "We got fuel flow now, Houston!"

The numbers are the progressive diameters. smallest 3 are the tip diameter.
The GM part numbers may may not be still valid.

sec rod chart http://www.hioutput.com/tech/qjetrod.html

 

thanks for the info! i'm putting the carb back on the car today after church, so i hope it does everything it's supposed to.

i'm running the edelbrock performer intake, but you know as well as i do, it's basically a stock replacement.

 

i put it on and it works! but it's lean up top still. i'll need to pick up some more rods, or try modifying a set. where can i get like a variety pack or something, lol! the weird idle issues and lean bog between 2800-4000rpm seems to be completely gone, but i can feel it really fall on it's face at about 4200rpm, and i believe this motor should be able to run up to 5000rpm without many issues...

also, if it sits for more than about 10mins, it's really hard to start, like the fuel bowl is draining completely or something like that. any ideas about that one?

 

Leaking well plugs.

 

oh...guess i gotta put some epoxy on them.

 

The hard starting after sitting is either the leaking wells and/or the plenum and carb fuel bowl get too hot. Blockoff the exhaust riser passages at the gasket.

The thin cast aluminum performer conducts the heat of the exhaust riser passage and heats the plenum way to well in the summer.
A wood QJET carb spacer helps a lot too.

 

That's Grimsrud.

He works at the same company I do. Unfortunately, in different locations, so I've only talked to him in person once. He has a restoration business on the side.

 

ok, so F-Bird said something about the needle/seat assembly being on the smallish side and that got me to thinking about my way lean condition. i determined that between all the sitting time and such that this car has done in the past, i would go ahead and drop a 10 dollar bill on a fuel pump. (i know, about broke the bank, lol! working at a parts store has its definite perks!) my upper rpm lean condition is NEARLY GONE! i mean, yesterday this thing would flat out NOT RUN above 4000rpm. it was strait up sucking the fuel bowl dry. i'm so glad that it wasn't the carb itself that was the issue.

i suppose because of the large fuel bowls of my holley and barry grant, i wasn't able to see the issue to this magnatude. the bowls are large enough on those carbs that the pump was able to catch back up before the bowl was completely drained.

now, the real tuning begins. i personally think that the carb works really well as it sits, but of course, there's lots of power and economy in tuning.

i also have the carb off the car right now as i'm sealing up the well plugs. hopefully that'll help with my hard starts.

 

MW, as long as you have the throttle base plate off of the carb you might as well check for the sec. throttle plates sticking in their bore. There is no throttle stop for the sec. throttle plates and they wear into the alum. bore and start to stick. The problem starts out with high milage carbs and is intermitent. This causes a real headace when trying to adjust the sec. A/V opening. The sec. T/plates are opened by a spring that is also used for the choke lock-out. A few years back we had a 406 on the dyno and could not get the sec's to open no matter what we did. I took the carb apart and I noticed that when the sec. T/plates opened they made a squeaking noise. I could see where they were wearing into the bores and thought that can't be it? I cleaned up the bores and plates and installed the carb on a car and it came back with the same problem and man you can sure tell when they not opening. I made a crude sec. T/plate stop ( see pic post # 36) that just opened the plates so they did not squeak and would not affect the engine idle speed. Problem solved !!

Auggie

 

Matt:
There is a tweak you can do, to increase float bowl size. You use a small saw (I forget the name for it now...) and cut the bottom bits off the black plastic thingie in the float bowl... I'm really having a brain fart, I can't remember the names of any of these parts, but i'm sure someone else can enlighten.

You can get a larger needle/seat, I think Edelbrock makes that part, and it's commonly stocked in parts stores. $11 or so.


And finally, you can also drill out the holes the secondary fuel pickups hang into. It's at an angle, so be careful. If you're interested in some of these modifications (drill and epoxy type of tweaks) let me know, I can always scan a few pages from THE book (doug roe).
Not for the light hearted. These are one way tweaks, so by all means try everything else first (rods/hangers/needle&seat/high flow filter etc)

 

ok, my secondary throttle plates are not sticking, that's not the problem i'm having, but thanks for the info!

i put the carb back on the car today with the epoxied well plugs. starting the car is now easier than ever! hold the key to start for .5 seconds and it's roaring to life.

however---the upper rpm lean condition is slightly worse than it was yesterday before the re-sealed plugs, but not quite as bad as it was before the fuel pump replacement. makes me think that it was drawing some fuel from the well plugs. now, the only way it's getting fuel is through the ports it is supposed to be getting fuel from. so...now i'm gonna pick up some more rods and the new needle/seat assembly probably next week.

this motor is only a 260 hp 350 crate, i don't imagine that it'll need any kind of REAL modifications. now if it was going on my 305 in my camaro, that'd be a different story, but i don't see any real benefit from that, lol!