i have a 350/350 combo in my 49.i can feel all those eyes of the flatheaders.well when i drive on a flat highway at about 55-60,that thing claters so bad you think it's going to fly apart.i talked to some people and they say lean mixture.some say timing.talked to an engine builder,he said distributor.checked the stuff he said and found its good.i unpluged the va*** advance and pluged the line and guess what no rattle.would this hurt anything to leave it unpluged.the drivablity seems fine.
What, exactly, is clattering? Is it a bad noise in the engine, or is the CAR rattling and you think it's being caused by the engine? Is it missing? Can you HEAR it in the exhaust note, or is the car shaking?
Yeah, there should be a couple of vacuum lines coming off the carb. One goes to the transmission, one goes to the vacuum advance. Try swapping them. What kind of carb?
at 55-60 it would be getting the same vacuum signal from the ported and non-ported connections on the carb, that's not the problem. Since the rattling went away when he disconnected the vacuum advance, it just has too much vacuum advance. Either back off the timing, get a different or adjustable advance can, recurve the distributor, buy higher octane gas, or just leave the vacuum line off.
What squirrel said X2 Also check for a stuck mechanical advance. Look closely at your balancer & timing tab combination. If they're mismatched or your balancer ring has slipped your timing light will lie. Does it have a hard time cranking when it's hot?
it has an edelbrock carb and intake.i bought an adjustable va***e advance,turned all the way in and backed it out 2 turns like instuctions say.turned out 10 turns and still there.they also say to put blue and silver springs on the weights.the rattleing i thought was lifter noise.more of a piston slap.i tryed premium gas and 104 octane boost.that did'nt do it.
Had the same problem with a Chevy ZZ4 350 crate motor. I modified nothing, just added carb, headers, etc. Closed off the vauum line and ran much better. Figured need some vacuum, so put inline a vacuum reducer (used for smog cars). Runs great now.
You should have mentioned that you had an adjustable advance in your first post! You probably need to put "slower" advance springs on the mechanical advance. Look at the ones you have, and put the next size thicker ones on it. Readjust the vacuum advance back to the factory recommended setting, too. Change that ( if you need to) after you dial in the mechanical advance.
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