guessing game so here's a guess. Blocked pilot jet although i'm sure that would have been thought of. Air screw [idle mixture fallen out]. Manifold rubber broken around boost bottle hose--or boost bottle damaged, unlikely i know. choke stuck open but choke [very small] jet down the hole in the bowl blocked so just sucking air [if stuck open]. Mmmmm--worst case, like my IT250K motor, the cylinder was broken around the base on the right side. That was an easy fix--i just put a genuine YZ465H motor in lol. Hell it goes!!. Forgot the obvious--crank seals which they were never hard on. Barrel base gasket sucked in, etc etc. Cheers. ps, float set so low it's only just keeping up with the main jet/emulsion tube and pilot sucks from higher up [by memory]. Next please?.