will 10w40 down a fuel injector resevoir on a 83 yamaha pw 50
 

hurt it? The bike did not run long with the 10w40 in it before i changed it to 2 stroke but it hasn't run right since. I would like to get this bike running for my son but don't know why it runs so poorly. It will start after a lot of kicking but will only run on full throttle and will not idle. If this is a carbueration issue what do I do. thanks for any input

I hate to say, but the piston and rings probably need replaced. The symptom sounds like very low compression. The engine oil probably did not cause the poor running, but 24 years is a lot of time on a piston that small. Your local Yamaha shop could check it out.