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In article ,
says...
I have a 1993, 25 ft. Searay. It's got a 7.4 Mercruiser Bravo (454
Chevy). It runs great untill I hit about 3000 rpm, 3/4 throttle, then
it hesitates, and sputters. I've replaced the 4 barrel carb,
sparkplugs, wires, fuel filter, and put in fresh gas. No improvement.
It seems to run good when running on two barrels, but when the other 2
kick in, the motor chokes. The local boat mechanic hasn't got a clue,
so any help appreciated.
Two things come to mind, not enough advance on the ignition timing,
and a messed up mixture on the secondary barrels. There is a possibility
of fuel starvation also for many reasons, bad fuel pump, bad section
of rubber fuel line, dented steel fuel line, dirt in or on the strainer
on the fuel pickup tube in the fuel tank.
Can you read the plugs a bit to see if it is to rich, or to lean. It
will nose over for either reason. If it noses over real bad due to being
to rich, you will surely see black smoke in the exhaust. I suspect
it is dying out due to lack of fuel, and that is when things start to
overheat and burn up. (like piston tops, valves, cracked exhaust manifold)
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