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Faulty Carb?

luhrs_40

luhrs_40

Contributing Member
My Port side 454 runs rough below 1000 rpms Over 1000 and wot shes good...Plugs wires timing compression is fine... Will the carburator be at fault? Vacuum gauge shows normal..Not only runs rough but makes the flex plate make funny noises ..By the way the flex plate was replaced and the transmission checked.. Any ideas? Thanx in advance
 
Probably is. Cap and rotor new? Starboard engine run good? You can aleays swap carbs engine for engine since you will be taking it off to rebuild it anyway.
 
Damper plates don't like an out of tune engine, especially at low rpm.

If the missing is that obvious, I can't believe the vacuum is 'normal'...maybe start with a good inspection and then try adjusting the idle mixture screws...
 
There is a good shake on the engine at idle comparing to other side... The air mixture screw it doesnt make any difference when turned..And the vacuum gauge flaxuates a bit at idle and then sits steady in higher RPMs, i will go over everything again before rebuilding carb..
 
Can you screw the idle mixture screws all the way in without the motor stalling? If so, the carb is flooding.

Jeff
 
Screw the idle all the way in and it didnt make any difference...Is that mean that the carb is flooding and the engine runs rough in idle only?
 
which carb is on top of the engine? If the rpm is high enough that the carb is running with the transfer port active, the idle mixture screws won't have any effect. have you looked into the throat of the carb with the engine running?
 
On a production marine big block, with a q-jet, if the idle is much over 750 rpm, the throttle plates are open enough to expose the transfer port. This means the idle mixture screws will have hardly any effect on the mixture.

Look into the air horn of the carb with the engine running...if you see fuel dripping into the primary bore on the side where the choke linkage connects, it is likely your fuel pump diaphragm has ruptured and is 'flooding' the engine...
 
..."On a production marine big block, with a q-jet, if the idle is much over 750 rpm, the throttle plates are open enough to expose the transfer port."

Like hell!

Jeff
 
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