Hey,
I had an overflow problem, too. Was with the Chinese Mikuni.
At first the engine wouldn't start and sometimes it did start. As sparkplug was dry I suspected dirt in pilot jet. Cleaned it a couple of times, but the starting issue remained unsolved.
I checked the float height with a transparant fuel line next to the bowl and connected to the (opened) drain of the bowl. Turned out the float height was to low. It was at the height of the pilot jet, so sometimes it was able to get fuel, while other times it couldn't.
I have changed the float height by bending the tab of the floater, where the needle rides on and closed the carb again. Well... it kept overflowing.
Opened the carb again to see what caused the overflow.
By bending the tap (down) of the floater, to get a higher float level, the bigger angle between the needle and that tab created "friction" when the floater was down in the bowl. enough friction to keep the floater down. At least that is what I came up with. Also the needle fitment is pretty loose sideways in this particular Chinese carb.
What I did to solve this issue: there are tabs on the floater that limits the floater to go below a certain point. I have bent them a bit, so the angle between the needle and floater tab are not creating "friction" at a low fuel float level.
The carb functions great now; no problems with starting and no more overflow.
