Sounds like the timing is retarded? Did you turn the engine over a couple of revolutions and recheck the timing position after your initial setting? I've never got it spot on at the first attempt. It usually takes me several attempts until I'm happy that it's correct. I will accept and settle for a tiny bit of over advance, but never a single degree of retard. Ron
Where I live in the summer it can get very warm and I have measured the cylinder head temp on my M21 at over 500 degrees. The temp of the oil tank was 175 degrees. Everything on the bike including the gearbox was too hot to touch. Bike does not mind and runs fine.