Thread: carb or ignition problem?

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Hey guys, Heres the engine..400sbc. new holley 4160 vacuum sec. timing set at 12 initial 36 degrees at 3000rpm. Cam is a crane .292/512 flat tappet. The engine runs fine at low speeds at this timing setting but when I punch the gas it just pops through the top of the carb. When I advance the timing it wont do this and actually provides the sound and performance I'm looking for. The problem is I'm over 40 degrees of total advance. I know you really don't want to be over 36 degrees on a small block Chevy. My engine just likes it more and it performs better. Could this be a carb problem? say a power valve or accelerator pump? I have already checked the floats and their good. When I advance the timing I can actually kick the engine up to Wide open throttle and it sounds great. I know to much advance can wreck your engine so I 'm a little worried. I bought a timing tape and installed on my stock 400 damper and verified TDC so that checks out. Any tips Anyone......Trying to get some performance here and be safe.

Thats a silverbird is it not ?It shoulda had the 455 and a 4 speed?

No they never came from the factory with a 455-and it's a tenth anniversary Pontiac Trans am. They either came with a pontiac 400 with a 4 speed or a Olds 403 with a 3 speed automatic. Do you have anything to add to the post or my problem?

What's the vacuum source to the distributor? Ported or manifold?

I don't have a vacuum guage but when I did have the vacuum advance hooked up it was connected to the ported outlet on the carb. The port near the top on the drivers side.
I eliminated the vacuum advance totally and plugged the vacuum canister on the dist. and on the carb. The car runs great now lots of power. My timing at idle is 19 BTDC and at 3000RPM it's 33 BTDC. Is it allright that I eliminate the vacuum advance? I've heard that you can but you will suffer poor fuel mileage. I don't think my balancer is bad though I've checked for true TDC already and everything checks out. Anyone....

i had same problem on my 400 two things you can do first is simple and works great disconect your vaccum advance and set you timming to 34 degrees at 3000 rpm you need to cut your timming back on the 400 because of the bore size.
second is get adjustable vaccum advance and adjust this to 34 degrees total advance at 3000 rpm. Another thing that will help is to replace the springs and arms on the mechanical advance so your total machanical advance comes in at 2200 instead of 3000.

Yeah I was thinking about getting a adjustable vacuum advance. Do I really need it though? The car runs great now without it. I have a MSD 6al does that matter?

no, but I would rework the mechanical advance this will help your engine rev faster