Transmission fluid or penetrating oil in the cylinder and let it sit a few days, then remove the pull start and turn the crank using a socket and bar.
Use only a moderate amount of force..too much and you'll break stuff and make sure to turn only in the direction if rotation!!
If that doesn't work you'll have to remove the head and hit the top of the piston using a block of wood and a
.
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)