I just got a running Honda 110 for $80 for my son. It runs well, shifts great, but it has a problem GETTING started. I can not get it started with the pull start for the life of me. I rebuilt it, new return springs for the dogs, all cleaned up, fresh grease, new coil spring, and fresh spark plug. It engages and turns the motor, but it won't start. I can however get it push started almost every time with as little effort as it takes to push start. And once it stated it runs great. What could cause this unusual situation?