115 HP Yamaha 4 stroke-problem

[dcholden]

Motor seems to run good at higher RPM's, WOT 5700-5800 RPM's. BUT idle the motor for 5 min. and then pull the plugs and they are as black as coal. I live in Loreto MX., so no dealer help. Local mechanic thought it was the control valve (part # 68V-14960-00-00) and I have replaced that $280 part with no improvement. The thermostat checks OK, the sensor for the water temp check OK, timing is OK. Any ideas on cause of problem? ps motor is 2001 thanks

[Capt Ahab]

Too much oil. Try 1/2 to 1 qt less AND use RingFree 1oz/10gal.

[slread]

I know that yamaha changed to hotter thermostats and different ECU on the F115s as mine were changed for not running hot enough (2000 model). That can affect spark plug performance. Supposedly the engine was not running hot enough at slow speeds to perform correctly. Search on "making oil" and you will find a plethora of info about this.