[iammarcuse]

I have a 1989 Yamaha 130. It runs perfectly but I keep fouling the #2 spark plug after about 15-20 hours. The plug becomes black and fouls out. So I am guessing that one cylinder is running rich. The pilot screws are all 7/8 out as per manual. The motor blubbers a little at trolling speeds but these high compression motors always do a bit. I have swapped to a NGK BR8HS plug which is one range hotter until I solve the problem.
Any thoughts? Rebuild carb? Reset float? Replace needle valve?

[iammarcuse]

Anyone have any real-life experience with this? How about you Rodbolt? You've seen it all. Thx kindly.

[iammarcuse]

TTT
Anybody?

[Doh]

I am not a professional, but I do run a 1997 130, and I would suspect.

#1 Swap the well used plug out of 1 of the good Cylinders. New plug foul easier than used ones.

#2 Needle and seat. Maybe not worn but may have the Red needle and seat Sealant stuck in the inlet side.

#3 Slim chance of a weak coil

[iammarcuse]

OK, thanks. I found some other posts with the same problem. I am going to spark test it first. Then test check valve on return line and finally clean carbs, set float etc.