I have a yamaha RT100 dirtbike that someone gave me, and it didn't run. well, I don't really know much about this dirtbike, but I cleaned everything real good, and got it to run. ran for about 3 weeks, and I guess the oil injector got clogged up, but I could hear the piston rings wern't getting good lubrication, so I didn't ruin everything. I opened it up and put a wiseco piston in it and premixed my gas, now it won't run for CRAP!. I let it sit for like 2 months, and now when I kick on it, it has really low compression. The compression was fine when I first put the piston in, and the head is on tight. I cleaned out the carb yesterday really good, took everything out of it, and soaked it overnight in cleaning solution, and it still won't fukin start. any ideas? Oh yeah, checked the plug and it has good spark.

 

You might have not done something right when you put the top end back together... Ring end gap ok? You should probably pull it back apart if it's low on compression.

 

I had an issue with a wiseco piston that did the same thing, it turned out that the little pin that keeps the rings in the right position had fell out causing a huge ring end gap and low compression. It's easy to check.

 

old piston = running (albeit like crap)
new piston = not running

I'd look @ the piston.

 

I still have the old piston, it's fine, but the rings are bad, would the rings from the wiseco piston fit on the OEM piston?

what clip are you talking about? I'm not familiar with that I guess

 

There's two pins, one on each ring grove of the piston. The ring gaps should be between the intake ports (one on the left and one on the right) and the rear transfor port windows. If not then there is your problem.