Not to put too fine a point on it, but you purchased a pig in a poke. Not only has TSK been out of business for several years, the MyStar 60 four-stroke conversion is almost unheard of.

You will need quite a few new parts to use a two-stroke engine. Mount, shroud, main gear/clutch pinion, are just a few that come immediately to mind. I'm just about sure you'll need new lower frames as well.

The OS 91 Surpass four stroke might work with your existing gearing, but the machine would be a dog, since that engine has far less grunt than the YS. In fact, TSK produced a kit to put the OS 91 in a MyStar 46, and it was a perfect match.

If anyone can help you, this guy can. Call Silas Kwok at (650) 591-0888.

Steve