Well, worst case scenario I'll grab a tiny drill bit and drill out the main jet, lol.
I'm gonna work on this today, the main plan is two clamps on the seat tube one on the bottom tube, and maybe a ring holding it to the bottom bracket via the crank axle housing threads.
It actually might be because of the 32:1 premix I used, and I'm not sure if its leaning out or choking up top, I think its choking because of the stock muffler with cat. It actually runs quite well until it seems airflow becomes restricted at full throttle or higher revs, because it doesn't hesitate or pop like its lean.
I think it's just the EPA muffler, this motor elsewhere is rated at 2.75 Hp and its rated at 1.5 by Predator, so I think tuning and the expansion chamber will make this motor great, well I know it will, these style engine are on every X1, X2, X6, push scooter etc. out there and there is tons of tuning info. I can't wait!