My way of testing them is a squirt of starter fliud in the plug hole, and if it fires or gives an attempt to start you can be fairly sure the problem is carby related or possibly as Max said the seal on the pull starter. I doubt this would be a cause because as you said in your first post that it was running.. Putting it in the plug hole means it doesn't have to suck fuel in through the crank, If no attempt to start as Tyler? mentioned, remove the muffler and look in at the piston and if you see any scoring then we have to consider it may have been straight fueld
