Sounds like it has a "chip" in there, in place of the points. Pull the starter housing and check for a postage sized part, stuck on in a "non-factory" way. It will have a ground wire and a wire going to the coil. There will be no wire connected to the points which are under the flywheel. Chips are commonly installed to "fix" bad points or condensers and can advance the timing to cause hard starting and/or erratic running. If so, you could try swapping the ground and coil leads on the chip to see if that helps. Or reconnect good points and condenser. If there is no chip, I would pull the carb and look at the reeds, they are held in with the same screws as the carb. No cracks, splits or bends allowed in the reeds. It might have a plugged muffler blocking exhaust or carbon build up in the cylinder too, raising compression.