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I have a 1994 Yamaha 9.9 which changes RPM on its own with out changing throttle position. It will speed up and slow down randomly, sometimes within 5 or 10 seconds or over a 10 minute period. I have checked for leaks in the fuel system. Could this be caused by changes in the auto choke position?
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Bob,
I don't think the auto choke would be kicking in and out. Make sure the fuel filter is clean - check the fuel line primer bulb when this happens. If it is not hard, then the fuel pump is trying to pull against a vacuum - check the fuel tank vent.
If the outboard has set up for four months or longer without running, the carb may be gummed up.
Remove the jet(s) and clean with Berryman's Chemtool. If that doesn't help, may want to do a carb overhaul, or try a shock treatment with Seafoam to de-carbonize motor and clean fuel system.
Good luck,
Ken K -
Thanks. I had it to a Yamaha dealer last winter and they supposedly cleaned the carborator and changed plugs. They didn't have the tank so if it was a problem there, they wouldn't have seen it. The vent is open. Thanks.Comment
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