I thank you for the input, it could been from riding in the rain I have some small holes drilled in the air box, there behind the body some what but in the rain the whole bike is wet. I do keep the oil changed and use prem gas in it but not to say that it won't have water in it. I have changed the gearing in the rear I'm running the same speed but with the motor turning less when running at full speed so much better as for the longevity.
Drilling holes in the air box is always a bad idea, since the original air box has very low resistance once you have removed the restriction between the box and the carb and has smoothened out rough edges and transitions.
Anyway, you should check that the valves are air tight. The intake valve can be checked by turning the engine to the start of the compression stroke, when the valve has closed and then pour a little fuel onto the valve. Now turn the engine through the stroke and look for bubbles. If there are any significant bubbles, it means air is escaping here when you compress your air/fuel mixture and that is a waste that lowers the pressure in the engine and therefore loweres power.
With the exhaust valve, you will have to put a finger up into the exhaust channel and touch the valve. Then turn the engine through the strokes and feel for pressures and suctions when the valve should be closed.
If they are leaking, you should remove the rust and re-grind them into their seats. If they are not leaking, you should still remove the rust, but re-grinding will hopefully not be needed.
Of course there is also a tool to check leaking valves called a cylinderleak-tester, but those can be costly when you might also need an adapter and a compressor (if you do not own one).
