RE: Worn out motor?
I always found one good test for compression is to hold the car up by the pullstart, if it stays up or slowly falls (grabs and lets go, grabs and lets go) then the compression is good (do this before running it) if the compression is low then it will usually stop running during the first tank of fuel when it warms up. Sounds like you may have an air leak that is causing it to run lean and hot.