I picked up a old Sig Mustang 450 and it had this motor with a tuned pipe. The side says YS 45 FS the other side says Made In Japan. The carb is really weird in that you can not see a rotating barrel. The 2 nipples went to the fuel tank, I think and I have no idea what that screw is on the bottom. Any info would help and any guess as to the value would also be appreciated. The piston and sleeve look like it was run very little if at all.

Thanks