The YS engines are not "turbocharged" but they are "supercharged" from the crankcase by the pumping action of the underside of the piston. ( similar to the current two strokes).

I have heard that just pumping air into the carb doesn't work, and it is necessary to mount a supercharger between the carb and the cylinder.

I think OS may have tried an external rootes type supercharger in the eighties, successfully, but it was too costly.

(If anyone thinks I'm wrong, - please say so, but also explain why you think so! )