Mercury 1998 150 efi

Old 04-29-13, 09:20 AM
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Join Date: Apr 2007
Location: united states
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Mercury 1998 150 efi

Lately my motor is extremely hard to start. Once started I can get it on plane barely but no full throttle. It will lower the rpms by itself then speed back up by itself.Once I get it going it runs pretty good even full throttle but not always. If warm it starts easy but still same problem with the throttle. It did get progressively worse over a 2 month period. Usually before my motor would start instantaneously if warm within an hour of turning off. I'm thinking bad gas, plugs are 6 years old. or the canister fuel filter is full of water that mounts on the motor upside down like a oil filter on a car. I've used Merc power tune every year on the motor but not yet this year. Any advise on how to trouble shoot this issue would be greatly appreciated. I do have ability and tools and change the water pump impeller my self every other year.
Thank you in advance , Jeffrey
Old 04-30-13, 03:46 AM
Join Date: Apr 2007
Location: Near Buffalo, NY
Posts: 4,233
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Your thinking is correct, especially if the boat sits for periods of time with ethanol gas in the tank.

Connect a portable tank with fresh gas to the motor and change the filter. If the problem goes away it's bad gas.

The signs of ethanol phase separation are water in the separator and/or reddish sludge in the filter(s). RPMs could be varying because of the water. If the signs are there, you have to drain & clean the tanks. In the future, if you must use ethanol gas, use a stabilizer (StarBrite, StaBil) made for it.

It also couldn't hurt to replace the plugs.

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