In my experience with pullers, if you need to put a pipe over it then you are at the point where the puller is going to break.
The flywheel shouldn't be this hard to get off. They are supposed to be held on snugly by the tapered fit to ensure that they are centered and won't wobble or come loose, but that is only frictional force of the two pieces being wedged together as the flywheel expands and the crankshaft compresses.
The problem with yours is that cold welding has happened at the molecular level between the aluminum flywheel and the steel crankshaft. Since they are both finely machined and pushed very close together, the steel atoms directly contact the aluminum atoms in enough places to set up metallic bonding, so in fact in a whole bunch of tiny little spaces, the crankshaft and the flywheel act like one piece of metal. Of course everyone knows you can't weld steel to aluminum, I just mean at tiny little points on the molecular level, they could never actually weld themselves together. This happens a lot with aluminum car rims on steel hubs. If you ever get it off, a light coat of anti-seize compound or oil or grease will prevent it from getting this way again.
Using a torch will work, as the flywheel is going to expand more than the shaft when heated, and greatly reduce the force needed to get the flywheel off. Just be really careful of the magneto coils inside. If you keep the torch aimed at the centre of the flywheel, and don't heat for too long, you should be ok. Don't give up if it doesn't work the first few times, keep trying and it should come off.