qwcrim!
You can do this by yourself and save money
A stock kx500 can have a piston too "short" and a barell too "long" when they fabricate the engine.
This make your squish-clearance way to far, if you are unlucky to have this "sort" of engine, you have some problem!
It will detonate under heavy load.
But if you reduce the clearance, the endgases on top of piston when it?s have been fired from sparkplug will not detonate and cause the pinging.
You can ask any tuner(E.G) if you don?t belive me.
It?s will cost you time and not money if you do this by yourself , maybe only buy a thinner headgasket!
But make sure not go less then 1,3mm!
(piston/headbanging).
Sorry about my bad english then