99Hawk120

Anyone familiar with these carbs? They're basically Qjets with the secondaries lopped off. I've got an electronic version on my Olds, and it's developed a weird behavior.

From the beginning:

Bought the car for $600. Car stalls every morning the first time it's put into gear. Always starts right back up and is fine. Figure the choke is messed and ignore it. Subsequent restarts were ALWAYS fine, even when the engine was cold. Warm starting was less than 0.5 seconds of cranking time

About 3 weeks ago, the car stalled on me after a panic stop and wouldn't restart. After getting the car pushed off the road, a quick inspection showed the choke plate had closed and jammed in that position. Took the plate completely out, started the car, and drove home.

After a couple of days I pulled the carb. On inspection I found the following:

Bent choke plate shaft was binding (replaced with choke plate and shaft from a junk Qjet)
Leaky primary choke pulloff (slowly let out over 30 seconds--replaced with known good pulloff from the same Qjet).
Dead choke coil (replaced with a part from junk Qjet).
Completely dead secondary vacuum break. (not replaced yet).

The accelerator pump is fine, and I replaced the fuel filter. Mixture control solenoid is fine, TPS is fine.

I have checked the operation of the choke from a cold start and it seems fine. Starts closed and cracks slightly open as soon as the motor is cranked. No longer stalls when put in gear when cold either. Hot idle drops down the way it's supposed to, etc, etc.

I have two nagging problems still. One is that the car shudders and tries to kill if I give it more than 1/4-1/3 throttle while the car is cold. This wouldn't be an issue in my Camaro, but 1/4 throttle in this car is anemic and not safe to merge into 50mph traffic.

Two is that the car now likes to stall on a warm start. It starts in half a second of crank, then stalls. Subsequent cranking will not start the car unless the pedal is all the way to the floor. Obviously the motor is flooding for some reason.

The dead secondary vacuum break that I didn't replace is a weird little beasty. It hooks into the choke linkage with a slotted arm (like the cruise control servo), and doesn't appear to be affected by any of the other linkage pieces. However, if you were to apply vacuum to it, it would force the choke plate open, my guess is even against the choke thermostat. I can't figure out whether it runs off manifold or ported vacuum (I can't see any possible use for it to run off manifold vacuum). If it runs off ported vacuum, what are the chances that replacing it would fix the first problem?

I can't see how that piece would cause the second problem, though. My guess is the reason it always started fine before was that the choke was open way more than it should have been. I'm wondering if maybe I have the choke adjusted TOO far.

Ideas? Suggestions?

85 Berl

I had the problem of stumbling and dying when you give it gas while cold. I had an 81 GMC truck with the same carb. I never figured it out, though. I replaced it with a Holley. I heard that there is a plug in the bottom of the fuel bowl that is notorious for leaking in Qjets and drains gas into the intake manifold. I know it can be replaced with epoxy, I just don't know exactly how. Any Qjet experts out there today?

Damon

Obviously you have studied this carb's mechanisms quite closely and have applied rules of logic and real-world expereince.
Hopefully, the following info will help you even more......

The secondary vacuum break should receive full manifold vacuum. How it works is this: The primary vacuum break (choke-pull-off) opens relatively quickly to keep the engine from flooding immediatly after startup. But the secondary break moves more slowly and pops the choke open even a bit further but a few seconds behind the primary. If you are unwilling the shell out the money for a new secondary break you can simply set the primry break to oepn the choke a little further, although it will usually cause a stall shortly after the first time you fire up on a cold morning. Second restart and it will idle fine. Net net- no big deal if you are willing to live with 2 starts per morning versus 1.

BTW- This may be related to why the car tries to stall if you give it gas on a cold engine. The primary pull-off may be opeing the choke more than the original one (you said you DID replace the primary pull-off per your post). A new choke pull-off DOES require that you adjust it for the proper amount of pull-off. The adjustment screw is obvious (right on the arm of the vacuum pull-off)- play with it 1/2 turn at a time using the first cold start of the morning as your tuning benchamrk. It takes the choke element more than 2 minutes in some cases to open the choke further than the vacuum break does- which makes setting the vacuum break opeing amount very critical to the first few minutes of running.

The warm restart has me stumped, however. If it started fine before it should start fine now. Is the choke staying fully open on a warm engine? If the choke element isn't getting either 12V to the choke element (electric choke) or hot air to it (hot air style choke) then it will tend to have the choke partially closed even ona hot engine whent he choke should be fully open. This is a long shot- I doubt if I'm on the track of the real problem here.

99Hawk120

Interesting. What would you say if I told you that A) this secondary vacuum break looks nothing like the secondary vacuum break on any Quadrajet I've ever seen, and B) both the one on the carb and the new one I just purchased do NOT hold vacuum. The old one doesn't move when a vacuum pump is hooked to it; the new one pulls in as long as I keep pumping the pump but won't actually hold vacuum. Obviously the old one is dead. I can't believe the new one is right either--it's effectively a controlled vacuum leak at this point (never mind the moving arm). I bet I got a defective one. Just verify for me that all pull-offs should in fact hold vacuum .

This is the closest picture I can find:



Yeah, I set it to the same as the original one; however the original one wasn't working right, so obviously this needs some adjustment. However, I checked and it doesn't seem to be opening the choke that far. I'll keep tinkering with it, but probably NOT until I get a working secondary pull-off.

Actually I think you are. I did some checking the day after I posted this. I drove home, parked the car, and popped the air cleaner off, and the choke was still open completely. So I waited ten minutes, and did a little test. If you just turn the key, it starts ok. If you so much as tap the gas pedal, the choke closes completely, even though the motor is definitely still warm. So, I think I was on the right track here, the choke is adjusted too "rich" (opens too late).

Damon

Sorry for the long reply time. Forgot all about this post.

Yeah, the vacuum diaphragms are supposed to hold vacuum constantly that I am aware of. There are a few that might have a tiny "bleeder" hole off to the side of the vacuum nipple. So I'd check for that before you determine you have a bad one.

The choke should not be shutting again 10 minutes after a hot shut down. Check the adjustment and voltage to the choke. I've seen it many times that the choke is heating from radiant engine heat just enough to get it most of the way open but still cause miserable drivability and hot start.

99Hawk120

There's no vacuum bleed hole that I can see. Rather, the back of the canister seems to have some sort of filter built in. I'll try and take some pictures of it tonight.

99Hawk120

Update:

The secondary choke pulloffs on these carbs do indeed "bleed" through the filter on the back. Verified this with a couple of GM techs... most the independent mechanics were scratching their heads.

So that problem wasn't a problem at all.

I adjust the choke a bit leaner, and the warm restart problem seems to be gone as well. I guess I got overzealous trying to fix the "stall when put in gear the first time" problem!

All's well that end's well tho. Total cost to fix: $0 plus some spare qjet parts I had lying around.