Most people don't realize the fit between the crankcase bushing and crankshaft is critical , it is a sealing surface and if it is too loose you run into problems. I have replaced crankcases on engines that exhibited poor performance and fixed the running issues.
tried to replace my front bearing in my kb 40 because of the same issue, and the new bearing,ordered from boca, came without a front shield and no groove to install a shield.stupid design.
The bearing in this engine was purchased by the owner from MECOA. It is s Chinese bearing with only one plastic shield instead of a rubber shield. Quite an inferior bearing. In upcoming videos I show this and what I replaced it with.
