2019 25HP Yammy. One Plug Fouling, the other is fine???????

[WayNorth]

Hi All: I have a 2019 25hp Yammy F25LWTC that is causing me grief. This has been a problem since new (yea... I know... but by the time I "knew" this was a problem... out of warranty, covid BS bla bla bla). The lower plug (2 cyl. 4 stroke) fouls after about 20 hours, the top plug remains clean. Plug looks a little oily/wet, not "dry" but black. See the attached pic. I switched the plug wires from the coil, bottom to top, top to bottom but the same plug still fouled. The motor runs poorly/rough, replace the plug and it's like new again. It's on a small boat, typically run at low rpm but not all the time. It gets opened up for a bit every outing... typically 5min. after an hour or so. If I have to bring it in, I will but if it's something minor... I'd rather no. We are in a remote location in Northern Ontario and getting things in and out is not so simple. Any suggestions/solutions would be greatly appreciated.

 

[SoCalAngler]

I have the same motor in a 2017. It’s new to me and I haven’t used it much. Perhaps a compression test may be in order. Also, try posting on the Yamaha outboard parts website ;https://www.yamahaoutboardparts.com/forum/general-discussion/yamaha-outboard-forum usually more traffic there.

Also, read this….

https://www.denso.com/global/en/pro...e-parts-and-accessories/plug/basic/diagnosis/

 

[racerone]

Reduce / lower oil level a bit ??