QJet bog on acceleration

[704spd402]

What could cause it to fall on its face when accelerating, almost like the 4 barrel is kicking in to fast. How do I adjust? Also when idling it wants to die when warmed up. This happens out of the blue? 70 MC 402 4spd quadrajet- new.. Please let me know what you think?

[Chevy Dave]

I would check for a plugged fuel filter, a bad accelerator pump, and a clogged air filter.  Also check to see if the secondaries are opening fully.

[704spd402]

Its got a different filter besides the paper one in it- brand new and air filter is brand new. I have another q- jet and have swapped. Completely diff when compared. The older pops and bangs when you are moving and let off the accel. The new Carb. is what I described. I could put anew accelerater pump in it. Also with either one it still dies at idling when warmed up right out of the blue. Driving me crazy cause i can't trust it! 

[Leghome]

I had a 68 Nova that had a Q-jet and every once in a while it would do that we never did figure out what was causing that to happen  325hp/327

[stangeba]

There is a vacuum diaphragm (white thing, bottom left) that controls the speed of the secondary opening. If it is leaking, unhooked or not working properly, this could cause your problem. This also opens your choke slightly after starting the engine cold, so it doesn't run too rich. (This is from my 71 350 4bbl stock engine. 

[cny first gen 71]

That is called the choke pull off and yes should be working.  Mine came apart one time but I didn't realize it another member spotted it at a cruise in.  Took it home and fixed it. Mine does the same thing but I attribute it to the fact I put the 4 barrel on and didn't do anything else. Just manifold and carb so I think it's just dumping to much gas for engine to handle at low rpm at higher rpm it's fine. I have a new cam and heads and other goodies to go on too eventually. 

[riverdogs00]

If the motor is warm, and the secondaries are free to open, then it may be that the secondaries are opening too early.  If the engine is cold, there is usually a lockout bar that locks them from opening.

This video (not mine)  shows the basics of how to adjust the secondary airdoors. 

 

[704spd402]

Ok thanks for the info. I will look into a couple things mentioned. Can somebody tell me how to adjust the secondaries if there is a way?-thanks!

 

 

[riverdogs00]

Secondaries I believe is mainly just metering rods for rich/lean, and air doors for driveability.    This is a great site for parts and info   https://quadrajetpower.com/

[stangeba]

Thanks!!

Great site and I found my 71 Qudrajet #7041202 and some great pictures.

You can clearly see the linkage on the side with all the Choke pull off rods and such.

I had mine rebuild in 1993 for $187.00 by the CARBURETOR SHOP in Ontario, Ca. because the primary shaft bushings were worn out and the throttle shaft would wobble when you wiggled it.