2000 Mercury 90 4-stroke missing

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KD4JKK

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Joined
Jul 30, 2003
Messages
2
I am new to boating and have just purchased a used Crest pontoon with Mercury with 120 hours. It misses hard and the power output is cut back considerably at any RPM above 3800,speed about 15 MPH. When this occurs, the RPMs swing up and down violently. If I throttle down, the problem immediatly fixes itself and the motor returns to a very smooth running. Dissapointing for my kids when tubing. I have put in new plugs with no change. I also have tried to trim differently, with no improvement. Motor runs extremely smooth at all speeds below 15MPH/3800 RPM. What Gives?
 
K

KD4JKK

Recruit
Joined
Jul 30, 2003
Messages
2
Re: 2000 Mercury 90 4-stroke missing

"Hey! that ain't no toilet...that's the gas tank!"<br />Thanks "Marine Doctor" for the fuel pump suggestion, the problem was indeed fuel starvation. Put the boat/motor in the repair shop and just got it back. Found more than two gallons of water in the gas tank...caused heavy corrosion in the carbs, and made the carb overhaul somewhat difficult. No doubt someone accidentally or deliberatly put that much water in the gas tank. The gas pickup is up high on the rear of the boat within two feet of the port-a-potty. My guess is the previous owner thought they were adding water to the port-a-potty. The gas tank was pumped down and cleaned, two inline fuel filters were installed to catch any remaining stuff that might have been missed in the gas tank. Boat now flies! Runs extremely smooth all the way up to 5500 RPM, about 25MPH which is great for a large pontoon. TO hell with fishing... were going skiing!!!
 
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