I'm just about done breaking in M3111667 myself.
I had it expertly installed and I am using Amsoil Saber pro. oil
I must say I have 0 overheating, no problems whatsoever, I hit 90kph on a sprint so far and thats with the stock aribox and carb.
I go up hills faster than 60kph if I want to and do 70 with my wife on the back.
I stay under 9000rpm with 7g weights and 1000 koso torque spring.
Koso variator, Kevlar belt, Malossi clutch, techni gas pipe.
However, if your stock 50cc engine is still mint(ish), go with 6g weights, 800rpm spring, remove the rev limiter wire on the cdi and you can hit 95kph.
I replaced my engine cus the bike I bought already had 20k so I figured it was time for a new engine and went M3111667.
Stock engine was still mintish when I saw the piston at the dealer. Oh well I have a spare.