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Hello SF

So I have a 03 500 classic touring and a few weekends ago we were coming back from a day out on the trails and it died, just killed like the stop switch was hit. Dragged it back home and check the spark fuel pump and compression, spark and fuel were good but compression was 30psi on the PTO and 120psi on the MAG.

Tore it apart and found PTO piston with a good divot in it and rings seized to the piston on the exhaust side. (Pics Below) I have new parts on order and the cylinders getting bored .50mm over.

The problem is I can't figure out why this happened. That side was obviously lean but why?

Here a a few possibility's due to conditions: It was rather cold that night around -5, questionable gas from a small bate shop/gas station, snow dust as we were on a long straight paved trail with 3 people in front of this sled.

Now other things that it could be from the piston diag guide in this forum: air-leak at the PTO side crankshaft seal, too lean carb jetting(Stock) or clogged jet as its stock, too far advanced ignition timing or faulty igniter box, too hot of a spark plug range?(BR9ES), too high of a compression ratio, too low octane fuel(91). In () is specific to my situation.

Judging by the info I have found I'm going to clean/tune and re-jet both carbs, check timing and inspect all parts that I can along with all new gaskets. I really don't want to crack the case the sled only has 3500 miles on it so I hope I can get away with out doing the seal. Is it common for the PTO crank seal to fail?

Anything more I should be looking into?

Can anyone tell me more by the pics of the piston cylinder and plug?

Oh and do I have to go up with jets due to over-sized pistons and any clue as to how much?





 
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