I am new to this forum, but recently purchased a 70 SS396 L34 that has been restored. Generally car runs well, but car lurches under hard acceleration like carburetor isn't smoothly supplying fuel. More specifically, I can accelerate gradually to 5000 RPM (don't have the nerve to go higher yet) with no issues at all, but if I stomp on it in any gear I get the same strong lurching response from the car like it is cutting out and trying to recover then cutting out and repeating that. I'm new to classic muscle car ownership and wondering if I can get some direction on likely causes. The car is original drivetrain but rebuilt and bored .030 with L34 spec cam and I believe Rochester carb. Does this sound like a carb problem or something more significant? Any help and direction to resolve is appreciated.

 

Rochester Quadrajets are notorious for the automatic choke closing when it's not supposed to,that could be your problem.
Try wiring it open so it can't close and do a run with a warm engine.
If the problem is gone you know what needs fixed,better yet get an Edlebrock intake and a Holley double pumper carb.
It could also be as simple as a fuel filter needing replacement,the Q-jet should have a filter where the fuel line goes into the carb and there may be an inline filter/s so take a look at all your fuel lines from the tank forward.
The Q-jet also has vacuum secondaries that are prone to failure,great carbs when they work right,horrible when they don't.
I always ran a Holley double pumper on my big block Camaro with a manual choke and manual secondaries,always went like a scalded dog when I stomped on it.

 

Thanks for the advice, I will give it a try. Interesting that you mention the Edelbrock intake and Holley carb set up as I’m planning to set this motor up similar to the L78 which I think would have those components and a bigger cam.

 

If timing and dwell are good,, adjust the secondary opening rate, meaning they may be opening too fast.
On pass side of carb, on the same shaft as secondary air valve rotates, there is an adjustment. It eludes me tools needed, but there is a lock screw/nut, and a spring-loaded shaft.
Loosening the lock device, have screwdriver on spring wrap-up, so as to not have the spring unwind, but no fear, one can adjust back into place, generally, there is 1-1/2 turns of spring wrap-up CW, and you might add another 1/2 turn, 2 turns total, and lock in place.
Wrapping the spring tighter, delays the rate the secondary air valve opens. You're looking for a slower rate of opening.
Keep track of the number/segments of turn on this spring and compare results as adjusted.

 

Thanks for the info, guys. These threads are going to be very helpful for me on this journey! Hope to have it running right soon.