When the day arrives when I can buy a VERY dependable China engine, I'll do it.
Until that day, I'll keep playing with my Tanaka and Mitsubishi engines. In 5 years, I have NEVER had to repair the engines.
When my CY460 engines quit breaking clutch springs, I'll reinstall them onto my bikes. Now that the manufacturer has knurled the velocity stacks, the air cleaner doesn't fall off this Chinese engine. The 460 has a reputation of burning the piston, due to faulty cylinder plating. That happened to me once; replacing the pcyl resolved that issue.
I run my engines center-framed with shift kit.
No need to go 4-stroke; just use a good 2-stroke.