Hi Graham,
Prior to installation, the engine was disassembled, and the case plus all adapter and venturi parts were soaked overnight in mineral spirits, and wiped down with 99% Isopropyl alcohol.
The first time I installed the adapter it was pushed all the way in, so it sat a little below the top surface of the carb opening. When I screwed the venturi in and tightened it very gently, it pulled the adapter up against the needle body, and broke the adhesive bond.
Disassembled and cleaned again, and reassembled with the adapter flush with the carb opening. Ran the engine, and found that the venturi had been drilled out for a pressure fuel system!
When I attempted to remove the venturi, the adapter broke loose again, and came out with the venturi.
Disassembled and cleaned again, and reseated the second adapter flush with the top of the carb opening. Gave it a couple days to cure the adhesive, and ran it on the bench. It started much easier, and ran great. On the last attempt to start it that day, it would only run out the prime, because the adapter had broken free again, and it was leaking air into the case!
I'm going to try it one more time, with thin gaskets to keep the venturi from bottoming out.
Bill