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84 9.8 mercury motor help


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hi since i bought this motor. at wot sometimes it sounds like it misses its driving me nuts. i was told maybe a spun prop took it off and got a different one same thing ive had it in 3 times to various techs this last time i lost power with it it died. the exhaust cover was sucking air they tightened it and it was good again but the wot it still seems to miss doesnt seem to matter if cold or hot. the compression i believe was 105 and 110 which i understand is good has had new carb the coil packs replaced they are used however i,m at wits end i paid 600 for it and now have 450 in repair bills any ideas i was also told it could be cavitating however it seems to do it more when i,m alone no extra weight so i put it on a buddies boat bigger one same thing. no one on a test run seems to think its bad however my wife can tell there is a problem please help should i junk it cut my losses and get a different one. it runs great other wise. also new fuel tank hose bulb etc and yes the vent is open thank you very much.

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Can you describe the miss a little more? Is it sudden (like rapidly flipping a switch) or does it seem to slowly bog down?if it misses and loses power, the engine rpms decrease and the boat slows. If it cavitates (ventilate is the correct term), the engine rpms will increase and the boat will slow down.

I will always hook up a timing light to each cylinder and listen and watch. If it begins to miss and the timing light goes out, I know its ignition. If not, I look towards the fuel system. The one thing not mentioned yet is the fuel pump. Has that been rebuilt?

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boat fixer it seems like a switch is quickly shut on and off for maybe 1- 2 seconds. it slows down then like a switch keeps going like nothing happened. it doesnt rev up when this happens. the fuel pump has been rebuilt. thanks so much do you think its worth fixing the techs say this motor is a electronic nightmare. also when its been fixed they put it in a tank of water always runs great they look at me like i,m nuts but when i put it in the water she does it.

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