48cc? maybe 4.8 CID?
I do think this is a hit and miss engine, even though the OP states it is "throttle governed"
Yes I am a member at
Smokstak.com.
This is a flywheel engine and I am not aware of a flywheel type engine with a motorcycle carburetor installed on it.
I really would like to help to get this project moving along, but I do not think a motorcycle carb is the solution on an antique cast iron hit and miss engine.
I did see video of this engine running with the Flo-Jet carb installed. Let's backtrack to the point when it was still running, and go from there, OK?