Question: Q-Jet Hesitation

[Vette79]

After my 79 Vette is at operating temperature and pressing the accelerator pedal to the floor quickly, she hesitates/stalls briefly. This is a new sudden issue. No work has been done and there are no leaks of any kind that I have found. Looking for some ideas......

 

[Barry08]

Check to see that your choke is coming off when it warms up.
Also check timing.

Barry

 

[Vette79]

Check to see that your choke is coming off when it warms up.
Also check timing.

Barry

Timing is good and I have an electric choke. I will have to look up adjusting an electric choke.

 

[Evolution1980]

Check/replace the accelerator pump. That's a fairly straightforward and inexpensive replacement. It might not be giving a good shot anymore. That was the issue with mine. Replacing it made a HUGE difference...completely removed the hesitation.

 

[2VettesMike]

It may be a good idea to also check the secondary vacuum opening valve. A leak in the diaphragm could let it open too quick and momentary bog the engine.

Thanks,
Mike

 

[shark454]

That type of hesitation is either from too much fuel or not enough fuel. Yeah, both conditions have a similiar symptom.. As stated earlier, look for vacuum leaks or worn accelerator pump. Vacuum leaks can be hard to find.

good luck!

 

[Vettehead Mikey]

It may be a good idea to also check the secondary vacuum opening valve.

This is the most common cause, the remedy might simply be a readjustment of the tension spring.

 

[Vette79]

This is the most common cause, the remedy might simply be a readjustment of the tension spring.

Thanks, will instructions for any of the suggested adjustments be in the shop manual or AIM? The Vette is in for the winter so I'm not in so much a rush as I would be any other time. But I do need to prepare...

 

[Vettehead Mikey]

This will give you the idea:

Hot Rod Horsepower Handbook - Google Books

 

[Vette79]

This will give you the idea:

Hot Rod Horsepower Handbook - Google Books

Thanks, Mikey. It doesn't seem to difficult and it doesn't appear as though you have to take the Q-Jet apart. I have little experience with a Q-Jet and am questioning whether my Q-Jet is properly configured for my application (Top-End Rebuild).

 

[78IndyPace]

Quadrajet Info

There's a ton of Quadrajet stuff out there. Do a search on "Lars Grimsrud Quadrajet" and you'll have much of it at your fingertips.

I had a problem like yours on my 78, and it turned out to be the tension spring on the shaft for the large air flaps above the secondary throttle plates that Mikey mentions. The spring keeps the flaps from opening too quickly. If these plates just flop open on your car (after it's warmed up and the choke has pulled off), that may be your problem.