Try squirting a little penetrating oil around the shaft, take the flywheel nut off, squirt some more penetrating oil and tap with a flat punch around the flat part of the flywheel and go all around the crankshaft that way. Don't hit the threads! Go have a coke for about 15 minutes, then come back and , lift up on the flywheel with a big screwdriver and give it a sharp whack on the nut! AFTER you put the NUT back on! Not all the way down, leave a gap. The flywheel should jar loose. I've never hit them hard enough to knock flyweights out before. You're not swinging a sledge hammer blow, just a sharp tap!