I thought I replied
things I've had success with:
1) put a lot of penetrating oil I. spray in the plug hole, through the intake, through the exhaust, and under the piston (pull it out as far as you can to spray from the bottom too
2) twist it. with the jug pulled off the studs, sometimes twisting gets more torque than yanking it directly off. don't go so hard you bend the crank, but that's not likely unless you're hulking it like a maniac
3) if all above fails, put the jug back on and use an impact driver on the flywheel nut (tightening). that impact should transfer to the piston and loosen it up a bit, allowing 1 & 2 aboev more chance of success. repeat in series it'll work more fluid in and work the piston loose.