I think it's always a learning experience on every build.
Yup, I'm also looking for vendors who can provide better quality engines. Well balanced, and centered cranks, fully ported, with reed valves, high compression piston, steel sleaved barrel, an angled spark plug on the cylinder head, and high speed bearings. Well, I guess that Vendor is still somewhere out there in the future.
Welcome to this exciting world of motorized bicycles...

It does sometimes comes with a lot of headaches, so have some aspirin ready...