I have a Honda GXV120 engine here, that has the same problem, that was on a SupaSwift Big Bob mower I got for $20, as a chassis parts donor. Don't think I'll bother resurrecting that one, though.
Aren't those engines prized or is that one of those OHC engines?
Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!