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View Full Version : Mercury Tech Sport Jet 90 loss of power. Need Help!!



madcap4
07-08-2008, 10:54 AM
I purchased a 3 cyl. sport jet 90 a month ago. Had problems with the carbs being dirty. Cleaned out the suction lines, got rid of the old gas and have ran 5 or 6 fresh tanks of gas/oil thru it, and occasionally a bottle of sea foam. I have a new battery, but only 2 new spark plugs. It starts up just fine and has run flawlesly until last weekend.

I filled up on gas at a station on the river and it ran fine for about 5 minutes and then the power just cut out. It starts and idles fine, but on WOT it doesn't go, it only stutters like its trying to go but wont. First thought was the guy gave me the wrong type of oil or not enough gas to go with the oil. I've ran another tank of gas through it but the mixture could still be off. Heres the funny thing. If I play with it in reverse, I can get the motor running good and then punch it foward and it takes off, but it will occasionally lose power again.

Besides the gas/oil mix, I think it could be related to the fuel pump. The manual says "A properly operating pump will deliver a constant flow of fuel from the hose. If the fuel flow fluctuates from pulse to pulse, the fuel pump is probably failing". Checking things out when I first got the boat, there wasn't a constant flow when I cranked over the engine. It was spitting out in intervals.

Sorry for the long post, just wanted to give the history of the motor since I've had it. Any help, suggestions, something I missed would be greatly appreciated.

madcap4
07-09-2008, 04:17 PM
Anyone????

Greg Moss
07-09-2008, 04:51 PM
water in the gas

madcap4
07-09-2008, 06:25 PM
But if there was water in the gas, wouldn't it not idle smooth as well. I did play around with the idle screws on the carbs though, but a couple days after it started loosing power, only to tweek them. If there was water in the gas, would it still idle smooth, or could I still get it to idle smooth through the carb adjustments?

Also there is white smoke coming from the exhaust. Is this a sign of water?