The moki should be run on 5% nitro at most mine runs best on FAI fuel 80-20. if you are running 16% oil you may have done some damage. I bought an older engine I ran on a bench few days later wouldn't turn over. It had an accumalation of sludge in the rear bearing where it had been soaked in cleaner. I disassmbled ,cleaned and replaced bearings still running fine.
Hopefully it is tight in the bearings. you should be able to see any piston=liner issues by looking through exhaust port or removing head. Be gentle with it Moki parts are expensive.