[beatr911]

For the air cooled Yamaha series such as yours, the 230cc variant had the long stroke. There would be some comparisons needed to determine which piston/rod combination would work and you'd have to calculate compression. The only really viable way would be to have scored a great deal on a spare motor.

Coatings can help control heat. I'd probably just do the exhaust port as there is alot of heat transfer in that area.

Clean and smooth the combustion chamber and piston. Clean up both ports of casting and machining imperfections while you're in there

Advance the stock cams. One full tooth will more than likely be way too much. Try like 5-10 degrees of crank rotation. Experiment. There used to be an offset woodruff key available for the TW200 but I can't find it now. Just advancing the stock cams will boost low/midrange - just what you want.

Don't shave the head. Advancing the cam will cause the intake to close sooner and increase dynamic compression. Increasing compression also creates more heat, so if it's a concern don't make it any worse than needed. Also shaving the head will bring the cam closer to the crank, retarding the cam timing - not what you want.

Jet properly using an O2 sensor and an air/fuel ratio gauge. You need this if you've messed with the intake or exhaust. You can effectively use a narrow band sensor because you want to be very near stochiometric anyway, maybe just very slightly lean no more than 15:1 at the most.

If you can get away with only one compression ring it will reduce friction.

Use a new copper core plug. Yup, less resistance than even iridium, just won't last 50,000 miles - but who cares? Widen the gap at .050" increments until you detect a miss at high RPM and 100% throttle, then close the gap .050. That is your ideal plug gap. This works on nearly all I.C.E.s really.

For spare motors look for the Chinese clone made by Zongshen. These are bulletproof engines, just like the OEM Japanese engines and all parts interchange with Yamaha. Since they aren't imported anymore, watch CL for the supermotard Zongshen Sierra 200cc. They are often dirt cheap. I had one for over 6000 miles and loved it. There are reports of over 40K miles with only normal maintenance.

If you have a balancer shaft, remove it! It adds internal drag to the engine and removing it will also free up a little power. Just locktite every nut and bolt on your bike!