It's a cheap engine with cheap spare parts. Runs great stockk too btw but inspired use of the dremel makes it better.
Cut away as much as you dare on the bottom of the sleeve to open up the channels. Chop away the skirt of the piston as much as you dare for the same reason.
Let me say... it responds well to this. It doesn't look pretty but it works.
Some grinding on the crank should be done too.
I'm feeding it 30% this year.