Timing issue?

Take the rear float bowl off. Turn it upside down. The adjust the float so that the top of the float is parallel to the top of the float bowl. Then go one turn (or a bit more) LOWER. Put the bowl back on. The float level should now be low. Start the engine and let it warm up a bit and then slowly raise the float until it’s up about 1/3rd of the sight glass and leave it.

IMO, half way up the sight glass is too nigh for most engines.