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Engine runs rough when we throttle up

We have a 40hp 2 stroke Yamaha engine on our boat. It ran great then it started to run rough when we would increase the throttle. It was intermittent at first, now it is all the time. We changed the plugs, new gas filter,carburtor was taken off cleaned and adjusted . It worked great for about 20 minutes then we shut down and anchored. When we were off on our way again it started all over. Could this be an electrical problem.

Please help,
Mike

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Sounds like a spark plug issue. If the spark plug is not torqued after a good number of months it can seep at high rev sustained pressure. Otherwise I would look at the spark compensator or possibly the float.

Posted on Jan 02, 2010

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Hello, It could be ele. If you have ran cheap fuel in it and it has sit for a while, I would clean gas tank,lines, carb again, and run prem gas in tank.

Posted on Nov 25, 2008

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