Quadrajet Choke Issues

[Bonnewagon]

I forgot to mention that you cannot expect the fast idle cam to drop down all by it's own action. You need to actually sit there in the car and tap the pedal occasionally so that the linkage is relieved. If you don't it will continue to run fast and when the motor gets hot, it will really go crazy. Remember that a fast idle setting when the motor is cold of, say 1500 rpm, will become 2500 rpm once it gets hot. The purpose of the vacuum break is too open the choke butterfly slightly so the carb gets some needed air once the motor starts. Most problems occur here. Too much air and the motor stalls. Not enough and the motor coughs and stumbles. That is why there is a spec in the manuals. Unfortunately stupid GM changed to a butterfly angle measurement instead of the good old gap measurement. No one has that tool to measure the butterfly angle, not even a dealer anymore. The best you can do is look up the gap spec on an older model and apply it to yours. Measure with drill bits. You can adjust the gap until the motor starts and runs strong under all conditions.

 

[airboatgreg]

Rule of thumb is the t-stat should just close the choke plate on the carb at about 70 degrees ambient temp and maybe 2 notches tighter. The linkage needs to move freely and the fast idle set properly. Usually at high cam, engine operating temp at 2100 RPM or so. QJet carb is an awesome dependable carb with a little quirkiness. The time lapse is great but the fast idle cam will only come down when the throttle has been opened as it is a mechanical hook up. If the fast idle cam comes down when the choke opens it is not set correctly. Something else to think about is the hot air intake to the air cleaner off of exhaust manifold. If this is not working properly the carb idle air ports in the base of the carb will freeze up at moderate temps and humidity making a stall condition. I can go more in detail if you want. The other issue is the vacuum choke pull off. Most only have a primary that should hold vacuum. Another words put a hose on it and put your mouth on the other end and suck... it should hold when you clamp off. Some have a secondary pull off that has an internal air bleed. Again, I can bore you if you want more info.

 

[Quadrajet Power]

Nice little time lapse explanation!

 

[pontiacgp]

The other issue is the vacuum choke pull off. Most only have a primary that should hold vacuum. Another words put a hose on it and put your mouth on the other end and suck...

all you need to do is to depress the pull off and then plug the vacuum tube with your finger. If it doesn't stay depressed it's defective

 

[axisg]

I think I may have mine sorted. My issue has been the fast idle cam sticks in the highest position. After looking at 2 of my spares I realised mine is not as loose as the others. On the spares you have a little wiggle room. The one on my car it moves freely but no wiggle room. When you top it out it sticks a little. I took off the choke assembly , put a thin washer in between the choke and the carb body. Discovered the cam would drop back down with this little shim. Took it apart, ground a couple thou off one side of the cam, cleaned it all up with carb cleaner, reassembled, and now it drops back like it should. Proof will be the cold start sometime this weekend.

 

[pontiacgp]

I like your post up until the part where your forecasting cold weather this weekend...

 

[axisg]

I like your post up until the part where your forecasting cold weather this weekend...

LOL, both me and my poor little dog have ragweed allergies. Cant wait for the first heavy frost to kill them off !

I hereby award 4 Internet beers to the AMC loving Oldsmoletick for the correct guess !

 

[airboatgreg]

A 38 special brass barrel cleaner brush works well for cleaning the choke housing. Try not to remove the green coating off of the linkage and do not use a lubricant. It should all move freely. Do not forget the importance of the hot air intake I mentioned earlier when cold as that will cause a stall, hesitation a quarter to half mile after a cold start. I have also ran into carbon build up in the intake and intake system that created cold drive-ability issues. GM makes an awesome carbon cleaner. X66A

 

[axisg]

Driving the car regularly this week. Other than being cranky for the first min when cold in the AM ( no stove pipe to the thermo valve ) its been working much consistently. With the AF gauge I have noticed its running a little leaner ( 13-13.5 ) than I thought it would. May give it a little more choke. Its so nice to be able to "fine-tune" the setting with this gauge. When I think of the countless hours I have spent setting these old carbs by eye, plugs, vacuum, glass of water on the intake it makes me shake my head !

 

[pontiacgp]

Driving the car regularly this week. Other than being cranky for the first min when cold in the AM ( no stove pipe to the thermo valve ) its been working much consistently. With the AF gauge I have noticed its running a little leaner ( 13-13.5 ) than I thought it would. May give it a little more choke. Its so nice to be able to "fine-tune" the setting with this gauge. When I think of the countless hours I have spent setting these old carbs by eye, plugs, vacuum, glass of water on the intake it makes me shake my head !

Those a/f gauges are a necessity....IMO

with regards to the mixture if your choke plate is opening a little too much that will lean it out