well if you put some oil in the spark plug hole and it started after that then i would sayn that it is low on compression as a coating of oil around the piston/rings/bore will stop the compressed air blowing by until it burns off.so this meand it will run for a few seconds then die.i would say that the piston has damage to the thrust faces and the rings may well be stuck in.take the barrel off and have a look at it they are easy to do just take the seat bucket out then the plastic cowl off from around the head then the exhaust and then undo the four 10mm hex headed 6mm bolts that hold the head and barrel on.
adam bike doctor
March 2010
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