Heres my dilemma. Rebuilt motor and new carbs 2 years ago. Replaced all fuel lines, fuel selector valve and main filter. Checked internal carb filters in spring and they were clean. Maybe 10 hours on rebuild. Had ski out first time over the 4th holiday. Started losing power at full throttle (55mph to 40mph with decrease in RPM as well). Runs fine otherwise. Pulled the plugs and the color is dark brown both sides. Compression 135psi both cylinders. I run Amsoil pre-mix 32:1(dont trust oil pumps) with 87 octane. I noticed 3 tiny pieces of metal wedged in the center electrode cavity. I've seen these before in other motors---melted piston! I pulled the RAVE valves to peek in. The PTO piston was fine - I can still read the imprint on top of the piston. The MAG piston is starting to melt. Now, what can be causing this OTHER than carb because I believe the carb is fine. I would rather troubleshoot other possibilities first being the carbs are new and the internal filters were clean and the plugs didn't show a lean condition. Any help will be greatly appreciated.
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98 XP 951 Cylinder Detonation
- Thread starter XPMIKE
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Either you are running lean from not enough fuel or you have a vaccum leak, Or you're not putting enough oil in the gas tank.
Dr Honda
Well-Known Member
Yep... that's either a lean run... or you set the squash band too tight. But... since it's been running for a couple years in it's current state... I'm going to say that's not it.
So... you could have lost a crank seal... or... since you pulled the oil injection... maybe one of the plugs came off the injection nipple, and you are sucking air. OR... the carb bolts came loose.
So... you could have lost a crank seal... or... since you pulled the oil injection... maybe one of the plugs came off the injection nipple, and you are sucking air. OR... the carb bolts came loose.
Thanks guys. The carb bolts are tight to torque specs, the cap is on the oil line nipple and and I know there is proper amount of oil in gas. One thing that confuses me is that every time I've seen a lean condition, the spark plugs would always indicate it and my plugs show normal running conditions. Is it possible that a lean condition exists and the plugs look normal (dark brown color)?
CASPX
New Member
I'm no expert but this could be possible as you are not doing a plug chop.
say your high speed was lean but your idle was fine you'd be baking the piston when riding it but giving it enough fuel/oil when ideling and since you don't shut it off without idling that could be how the plugs are getting wet.
Just a theory to possibly answer your question.
say your high speed was lean but your idle was fine you'd be baking the piston when riding it but giving it enough fuel/oil when ideling and since you don't shut it off without idling that could be how the plugs are getting wet.
Just a theory to possibly answer your question.
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