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1995 Mariner 40 hp 4 cylinder 2 Stroke running 50%

P

parri1tb

New member
I need help guys
The boat cranks and idles great. Runs good for about 5 / 10 minutes then drops to about 50% power. You can push the Key choke and the motor runs about 80 / 85% then returns to about 50% power. I changed the gas bulb, gas lines and fuel pump. The motor seems to run a little longer at 100% but then goes to about 50%. I have taken the carbs off and cleaned. Saw nothing, they actually looked very clean to start with. Before I put the carbs back on, I thought i would ask about any adjustments on the carbs or any other ideas anyone might have for me. I'm stumped! Help
 
Sounds like lean out. I suggest a fuel pump rebuild including hooking up a pressure gage temporarily before the carbs.

Jeff
 
Thanks for the reply Jeff but I did put a brand new fuel pump on the motor 2 weeks ago but have not checked pressure. Maybe also I should have used gasket sealer on the fuel pump gasket. Maybe it's loosing vacuum at that point???
 
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Might be. I've seen brand new FP check valves screw up, so...

The pressure gage reveals what's going on (IF it's fuel related). You should see at least 5 psi at speed.

Jeff
 
I believe the fuel pump operates on pressure pulses and not so much on vacuum.-----The motor performance improves with operation of choke / enricher and that points at a carburetion issue.---- Or test run with another tank and hose.----Possibly water in the fuel.
 
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