2019 25hp Yamaha Fouls lower plug but not the other ?????

[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). Here is what I know:

• 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 like a POC, 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 not. We are in a remote location and getting things in and out is not so simple. Any suggestions/solutions would be greatly appreciated.

 

[racerone]

One plug looks normal.----The one clean plug looks like there is no spark !----Time to do some testing.

 

[WayNorth]

Thanks for the input. I did switch the wires (without switching them at the coil) and the same plug fouled. I'm pretty sure that the "new" looking plug is getting fuel, it purrs like a kitten with new plugs. Suggestions for testing would be appreciated!

 

[flashback]

Might want to try a new plug.

 

[WayNorth]

Thanks flashback... I've changed the plugs 4 or 5 times, twice with premium plugs. 20 hours (or so) and the one is pooched even though it doesn't look that bad.

 

[racerone]

The plug is NOT fouling.----Do a compression check.---Check valve clearance.--Check operation of fuel injectors ?

 

[99yam40]

have you tried to swap the plugs to see if the clean one then worked in the bottom hole and the dark on works in the top hole?

how about checking spark with a timing light on both plugs when running good and when not running good?

 

[WayNorth]

The plug is NOT fouling.----Do a compression check.---Check valve clearance.--Check operation of fuel injectors ?

Thanks for the suggestions, now all I need is a lake that isn't stiff on top

 

[WayNorth]

have you tried to swap the plugs to see if the clean one then worked in the bottom hole and the dark on works in the top hole?

how about checking spark with a timing light on both plugs when running good and when not running good?

Thanks, I have tried swapping the plugs. It runs but eventually the bottom plug fouls as well and then it runs "extra bad". Thanks again for the suggestions.

 

[racerone]

The plug ( lower ? ) shown in post # 1 is not fouled in my opinion.----Do some trouble shooting.

 

[99yam40]

Thanks, I have tried swapping the plugs. It runs but eventually the bottom plug fouls as well and then it runs "extra bad". Thanks again for the suggestions.

still need to see if one or both are getting spark when it runs bad.
Have to eliminate what you can from being the problem, to search for only what truly is the problem.
as I said an inductive timing light will show if spark is happening and if it is steady and it can show you if the timing of that spark in in spec while problem shows up

did you try cleaning the plugs?

as was said already the top one does not look like a normal plug that was burning fuel, the insulator should have a tan color like the bottom one.
But not sure if the real dark on the rest of plug is normal.

maybe the top one is getting steam cleaned from water ingestion

 

[flashback]

I think you're running on one cylinder.

 

[WayNorth]

Thanks for pointing me in the right direction guys... soon as my fishin' boat is up and running I will get on this, I've been waiting about 8 months for a 50 Merc lower end seal kit... crazy times. 8 months (so far) for a piece of rubber???

 

[99yam40]

if you are still waiting on the seal, why not work on this problem to get it taken care of?

 

[WayNorth]

if you are still waiting on the seal, why not work on this problem to get it taken care of?

Because... camp is 200km,125 miles north of here and the lakes are pretty stiff right now I can wait to get back, ice-off is typically early May so everything gets put on hold for now. Except the "asking questions for later (May) part".

 

[99yam40]

should have brought the project motors home with you to work on during the winter.
poor planning