This is a wild shot.... Sometimes these engines will run just on fuel draw; like a glow engine carb. Are you sure your pulse holes are lined up and working, and that the fuel pump is working? If the fuel pump is working, no attitude change should make the engine run differently.

Are you positive that Zenoah carb adapter is feeding a crankcase pulse to the carb fuel pump??

Also, if you are not running a primer bulb, there should be only one fuel line to the carb; the one from the fuel tank clunk to the fuel line on the carb nearest the fuel pump. If there is another line fitting on the carb, it was for an external primer bulb, and it needs to be blocked off.

AV8TOR