Don't have a piston. They are sold in several slightly different sizes so I figured I'd measure first and order the closest size. I'd appreciate the bore measurement.
Not overly concerned about the low compression as long as it runs nice. Do you have the left over base gaskets? I don't seem to have them in any of my parts boxes at home. Wouldn't be the first time I accidentally threw some good parts out while cleaning up (just the other day I threw out part of a PC case I needed thinking it was just a chunk of scrap metal, DOH!).
Riding to work on Friday it seemed just a touch low on power but I didn't really pay attention to it. On the way home it seemed much lower. Seems to have lost all the "punch" at higher RPM and it doesn't want to redline in first anymore. Stalled on the road at one point. Seems to sputter a bit when I first get on the throttle sometimes. I changed the transmission fluid on Thursday but I can't see how that would affect it unless maybe I over filled it but I put in 600cc as per the specs. Seemed to be running a bit hot lately, too, but it was only a problem when stuck in traffic. Came within 1 bar of the highest on the gauge at one point.
Over the weekend I cleaned the air filter for the first time and finally got around to checking the setting on the oil pump. Air filter was barely dirty and is surprisingly annoying to get in and out and took forever to dry between cleaning and oiling. Had to drop the oil tank in the back to get to the rear air filter bolts. Luckily it's only held in with 3 screws (and 1 was missing, lol). Oil pump was set way too high so I lowered it. Dumped a can of SeaFoam into the tank to help clean out any junk but I have no idea if that ever makes any difference. Took a look at the spark plug and it was looking pretty grimy but I didn't replace it yet. Might grab a replacement on the way home if it's carried by PartSource/Canadian Tire. Took it for a test ride Saturday night and again it stalled at one point.
Rode it to work today (avoiding the highway). Still didn't want to rev up at first but seemed a bit better by the end of the ride but still down on power. Will double check compression today if I can (should've done it on the weekend, not sure why I didn't) and maybe try changing the plug. I still haven't changed the power valve, which you mentioned to me looked like it was wearing and needed replacement (plus it had a gouge in it from when the rings blew up) so maybe it's an issue with that? I have the replacement valve and seals but I don't have a new gasket or spring. Not sure if I need them. Power valve is tucked behind the radiator so might be hard to replace without dropping the rad, which I'd rather not do.
I thought maybe it was a clogged air or fuel filter but the air filter seemed fine and cleaning it made no difference and I can't find a fuel filter on this thing or in the parts list so I don't think it has one. Only thing it has is some kind of vacuum valve on the base of the tank. No idea how that works or what it does but it seems to still be connected properly. There's a large air bubble in the fuel line I couldn't get out but I think that's been there for awhile and didn't seem to ever hurt anything before.
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