2003 Yamaha F225 Spark Plug Insulator Nose Dark

[johnfbushjr]

Just changed plugs for the season and noticed the plug from the top cylinder, port side had a noticeably darker insulating nose than the other five (see picture). 125 hours on them. Any thoughts on what may be the cause? Is this a common issue with this engine?

 

[johnfbushjr]

To clarify there are 125 hours on the plugs ... about 750 hours total on the engine.

 

[Brent]

I.dont see the pics probably my phone

I.think if brown then fuel mixture is lean

Maybe fuel injectors need cleaning

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[Brent]

Maybe time to clean throttle bodies, too with spray and manually cleaning using small brush and a shop towel probably has oily film

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[johnfbushjr]

Sorry the file didn't upload the first time ... too big.

 

[Briand31]

Could be several things bad plug, injector spray pattern, coil failing, compression in that cylinder low, first off I would start with a compression test on all cylinders. Plug is rich seems to me that cylinder is not firing.

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