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Engine cranks ok but at 700-1100 rpms tends to periodically backfire/cough thru the exhaust. This happens about every 4-5 seconds. Also while at dock, seems to have excess unspent fuel on top of the water all around engine lower unit. Engine runs fine once underway thru 5000 rpm. Any suggestions?
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Sounds like a little too much fuel is passing through one or more of the carb throats at low rpms. Or the idle jet of one or more of the carbs is clogged up with debris. Take the air cover off and look into the carbs at the rpm range you hear the coughing at. The float level is probably a little too high on that carb or the float needle is getting worn out and can't regulate the fuel level too well anymore. If you haven't done it already it may be time to rebuild the carbs and give 'em a good cleaning out. Pay particular attention to the idle jets and their passage, and the main jet and O-ring seal on each jet. The larger brass bolt looking thing at the bottom of each carb bowl is the main jet, the smaller looking one is the idle jet. Yamahas are infamous for carb jet clogging. If you don't have one already you can go to www.YamahaPubs.com and order a service manual for your motor and they'll mail it to your door. Good luck.
Mike ......... Miami, FL
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