- Lack of compression.
- Power-valve limited operation.
I stripped the top-end of the engine down with it all still fixed in the bike frame, which made it a quick and easy job. I found the restrictor-plate has already been drilled out of the exhaust and the carburettor too, so that's saved me a bit of work!
The piston and rings looked ok, with a little scoring to the front and rear faces, which matches the score marks to the cylinder-wall, shown in the pic below. I can just about feel the score marks on the piston itself so for what the cost I will be replacing it, but they cannot be felt at all in the much harder cylinder-wall. The scoring, along with a distinct lack of soot leads me to believe the engine has been run with too little 2-stroke oil in, probably through error, but possibly due to the oil-pump not being able to delver enough to the de-restricted engine, particularly if the carb. has been up-jetted. I will check to see if this is the case before ordering a set from Dell'Orto.
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