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Old 05-28-2001, 07:00 AM
JoeGrapes JoeGrapes is offline
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when I check the vacuum on my 440 I get a reading that bounces between 10 and 12 inches at idle. As the motor is reved up, it will keep bouncing plus or minus 1 inch. Never steady. The motor has .284/.484 MP cam, headers, Performer RPM manifold, 750 Holly and MP ignition. I know my comp. is too low for the cam, about 8.75 with pressure at 150lbs. I'm going to us Rhoads lifters. Is this normal with a longer duration cam? Or something else wrong?
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Old 05-28-2001, 09:19 AM
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1969RR 1969RR is offline
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Cool vacuum on 440

THis could be a few things; Pulsating vacuum means one or more of the cylinders has a problem. Could mean poor valve timing due to incorrect adjustment, a worn camshaft lobe, collapsed valve lifter, leaking, worn cylinder bore or piston rings or leaking head gasket. There are other tests that you can do to nail down were this is coming from.
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Old 05-28-2001, 11:25 AM
CaptNemo CaptNemo is offline
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A valvespring could be weak as well, how much use is on the springs?
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Old 05-28-2001, 02:15 PM
PRO PRO is offline
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It usually means you have a leaking valve,past the seat allowing reversion in the intake,you could also have a valve that is not fully seated due to an over adjusted rocker,that is compression is escaping back into the intake manifold youll need to perform a leakdown check to determine which valve is at fault.........PRO......
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