bkruse,
One thing you need to know about the KX500 is that you will never be able to eliminate the engine surge. By "surge" I mean when you close the throttle the engine speeds up and slows down a few times until finally settling into an idle. Some people have tried to reduce this via jetting changes. I think the majority here believe that this is natural to the KX500 engine. Some also believe that this indicates that your jetting is close to ideal. I feel that my jet setup is correct and my engine surges.
My bike is a 2002. Everything is essentially stock (pipe, reeds, etc...) except for the jetting.
Stock 2002 KX500 Carb Setup:
Main - 168
Pilot - 58
Needle - N82M - 3rd from top (i.e. middle)
Slide - 7
My bike ran horribly with the stock jetting!!!!! Especially poor from idle to half throttle.
My changes from stock for 1000 FT:
Main - 170
Pilot - 52
Air Screw 2.5 turns out
At 2.5 turns out the air screw just barely affects the idle. This would indicate that the pilot jet is still too large. However, I will not go any smaller. The bike needs fuel flow for lubrication when the throttle is closed. I want to stay on the slightly rich side. My throttle response from idle is excellent. I've never needed to think about carrying a spare spark plug. It starts on the first or second good kick and once completely warmed up it runs fantastic.