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Old 04-19-2006, 05:20 AM
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Engine lopes in Gear

My 74 Firebird with the 400cu engine has a problem when it's in gear. When you put it in gear the engine revs up and down from 550 rpm to 800 rpm. Now I've played with the timing, adjusted the idle screws and checked for vac leaks with no change. The motor has a 4bbl, mild crane cam, and headers/flowmasters which keeps it a relatively stock engine. Any help on this would be greatly appreciated.

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Old 04-19-2006, 07:10 AM
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how long has it been doing this? have u made any changes to the car since u noticed this problem?
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Old 04-19-2006, 01:01 PM
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Have you checked fuel pressure at the carb inlet? Should be 6 psi max. Just a thought, but it might be dumping raw fuel in and causing the motor to cycle.
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Old 04-19-2006, 01:58 PM
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Is your AC or defroster turned on? Perhaps the compressor is cycling, and the idle solenoid is whacked.

Pat
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Old 04-20-2006, 06:17 AM
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If you've already checked for vacuum leaks, and you it's not a compressor problem. You're dealing with either fuel or ignition. It should be somewhat easy to diagnoise what the engine wants at that point.

Put some wheel chocks in front of your front tires, and have someone sit in the car WITH THEIR FOOT ON THE BRAKE now when the engine is surging up and down press on the accelerator pump of your carburetor without moving the throttle linkage. This will add fuel without changing the volume of air that goes through the carburetor, and let you know if you're running too rich or too lean causing this problem.
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Old 04-21-2006, 05:04 AM
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Well there is no AC in this car so that's not the problem. The car has an electric fuel pump that might be giving it too much fuel pressure? Maybe a pressure regulator should be installed. It was doing this a bit before but now that I've made some timing changes it's more evident. I'm still thinking it's a fuel problem more than a ignition problem. Well I can't do much for the next few days got other things on the go but I will get back on this and let you all know what happened. Thanks
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