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Old 09-08-2007, 11:56 AM   #1
t/a 6.6
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1978 Trans Am Help

I have a 1978 trans am, with the pontiac 400 motor with the high compression heads(350). The car was running great untill about four days ago. All of a sudden it started bogging down real bad, and shutting off. I have already rebuilt the carb on it, I check the distributor and it was fine, and just took off the intake manafold and the gaskest were fine. Could anybody please tell me what else could be wrong. It is acting like there is a vacum leak somewhere, but i can't seem to find it. Any Ideas?
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Old 09-10-2007, 08:52 AM   #2
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Re: 1978 Trans Am Help

t/a,

Initially, it sounds like a fuel delivery issue. Be certain your fuel filter(s) are clean. Did this problem show up immediately after you changed the carb? Fuel pressure? "Sock" in the tank? More detail, please. Maybe I can point you in the right direction.

Jim
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Old 09-10-2007, 03:44 PM   #3
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Re: 1978 Trans Am Help

it was running great four several months after i rebuilt the carb. I put gas in it and it started running like crap. I put some dry gas in it and tryed to run it out. I put a new batch of gas in and it didn't fix the problem.
What happens is the car refuses to idle. When your at a light it will shake real bad then shut off. I have to keep it at about 1000 rpm to keep it running. And when you are moving it shurges real bad.
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Old 09-11-2007, 08:25 AM   #4
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Re: 1978 Trans Am Help

DEFINITELY fuel. The "surge" comment nails it. Perhaps the bad batch of gas injected water into the "mix". That can destroy the nitrile float. It can also "scale up" the innards. Did you replace the float when you rebuilt the carb? Did you use a stock replacement, or a brass one? If not, GET the brass float! Borg Warner and NAPA can supply the float.

Also be certain the "sock" on the pickup tube is not collapsed. Check the fuel filter closely, too. If air bleeds in the carb are clogged, that will cause the idle issue.

A fuel pump test could also be in order. Use a vacuum guage on the suction side, to be sure. Once you KNOW you have vacuum there, do a "volume" test, by filling the fuel bowl and running the engine, with the discharge hose from the pump going into a safe container. 15-20 seconds of running time should get you at least 1/2 a gallon of gas into the container. If you have no (or under 6") vacuum, replace the pump.

You can "test" the sock by blowing compressed air backward through the fuel line, removed from the pump. Be sure to remove the gas cap before you try! (:-

Keep us informed.

Jim
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