Hey guys I need some help. My engine wants to die at part throttle. Usually around 2,000+ rpm. This dosen't happen all the time but, it's making it hard to drive. I changed carbs to another q-jet and still the same problem. It ideals around 700 with my timming at 12 degs' w/advance removed. With the advance hooked up and steadily reving the motor to 2,000 I notice the timming mark jumps. Not making a steady advance transition. Accorrding to the chiltons this could be an improperly operating mech. advance. What do you guys think. Its a stock 77 350 except for a stock aluminum intake and newer used stock parts.

I'll assume for the rest of this response that the carb is working properly and fuel pressure is OK- I'll just make ignition-related diagnosis....

Getting a stable, repeatable and accurate timing curve is important to a stable and consistent idle. This means it MUST drop back to the same base timing setting all the time, every time you drop back down to an idle. If the centrifugal advance is "sticky" (very common in older HEIs, for example) or the centrifugal advance springs are weak/broken, it's entirely possible you set it at 12* but SOMETIMES it drops down to the true fully-retarded base position, retards the timing from where you set it and it dies. You THINK you're at 12* initial but in fact the centrifugal is already slightly up the advance curve when you're setting the timing. When it does, from time to time, drop down to the TRUE base position your base timing is suddently retarded from where you think you set it and it doesn't want to run.

Now, if you're seeing fuel spew out of the carb or some other obvious flooding-related problem, then certainly fix that first. But one of the old rules of tunign and engine is that you make sure your ignition system, base timing and advance mechanisms are working correctly before you start fiddling with the carb. Can't tune squat until you have a strong, correctly timed spark.