I have a 1970 HT1 90 I'm working on. It was a basket case and a money pit, and this is my first 2-stroke project. It has extremely Low compression and of course won't even fire. I've honed the cylinder and installed a new piston & rings (2 rings). It's already been bored 2 over. I'm missing something here and am not sure I can even bore it out again as it's already 2nd over. It does get a good spark .    Any suggestions? Thank you!

Hey, I'm not sure I understand your post. Your old cylinder had low compression? I can understand that, but are you saying you bored the cylinder and with a new sized piston you still have low compression - something not right there. You could just get a better used or new head and piston and be good to go. Nowadays with lazer welders and so on everything is almost rebuildable if you want to spend the time.
Dude's like lowbuckgarage are always finding a route that gets the thing back on the road - and remember 'if you aint having fun you aint doing it right'

Yamaha have four oversizes , so you still have options .