Once it's started it runs okay. It take a couple of dicey pulls to get it to fire, but once it's going it's fine. I don't think its a backfire, because there's no backfire from the engine. It just yards the pull start out of my hand like it has a serious recoil. The coil spring is not over wound, it just seems that the pullstart doesn't disengage after you've pulled the cord. I use to be able to pull on the starter and if the bike didn't start it was no big deal, but now it whips the starter out of my hand, and it loosens the bolt that holds the disc and coil spring in place. I've put everything back together the way is shows in the schematic... it just doesn't disengage after each pull.
