Hi all, I have just installed a rebuilt Rochester Quadrajet onto my 72's rocket 350. I had my mechanic friend stop over and set the idle and fuel mixture and the engine runs great with a perfect idle and response. But I have one small issue I'm hoping I can get some guidance on and what to do. When I'm at a full stop, the idle is fine but when I step on the accelerator to head down the road the carb has a hesitation for a brief moment as if it wants to stall, but then runs fine. Do I have to adjust one of the carb screws for just throttle response? Not the air fuel mixture screws but possibly another location?

 

Did they replace the carburetor accelerator pump during rebuil? What you're describing is a common symptom when an accelerator pump is flaky. There could be a different issue, but that's a good place to check.

 

To check the accelator pump, check for two streams on the primary side when you open the throttle with the engine off. Under heavy throttle, it could be the secondary side.

 

Thanks Guys, It is an original date coded 7042250 NC - 3151 that was professionally rebuilt, I checked all vacuum lines and they are tight. Could it be the throttle adjustment screw is off or the choke adjustment screw?

 

Is the choke fully off?
What is curb idle RPM?
As mentioned verify the pump shot is strong.
Engine off, full stroke the accelerator...you should see two strong squirts down both primary venturis.

Which hole is the pump rod installed into the pump lever?

Light throttle tip in or heavy to the floor boards bog?

What is the manifold vacuum signal reading at idle?

Did the re-builder install the third center (power piston) adjusting screw?

 

It probably is related to the accelerator pump as other members mentioned.

Tell us more, why was the carb rebuilt, how many miles on the engine if known, is the distributor original, dwell in spec, ignition timing in spec, timing set replaced, compression test done?

It is common for the carb to be blamed and sometimes it is the culprit but other things also have to be correct.

 

It is possible to adjust the accelerator pump timing and shot length by bending the link, but do this carefully. There is a spec number for setting this. Of course this assumes the pump cup is in good shape. Many of the aftermarket replacements today are crap, so even brand new is no guarantee.

 

Make sure the fuel squirts out of the accelerator pump with the slightest movement of the throttle.

If not, inspect the accelerator pump piston. The quality of some replacement parts are junk, if in doubt get one from Cliffs Q-Jet. Inspect the seat under the tiny check ball, make sure it’s not pitted.

 

When going down the carb rabbit hole, its always good practice to make sure everything else is up to par- the tune up is good and the timing is set properly and the advance is working as it should. Of course checking for vacuum leaks as well. Otherwise you might be chasing your tail.