The target drone engines don't have serial numbers stamped anywhere. Most of them have a raised impression of ":91" on the backplate.

I met a guy who has a drone sportster .65 and swapped carbs on my engine. It throttled normally. The other engine I borrowed the carb from was a drone engine as well. After trying a few things, I think the hole in the brass tube inside the barrel is too big.

With the other carb, it throttled like a dream. It also idled at 2200rpm for 20+seconds with a 13x6 APC.