I’ve owned a few KX500’s, mostly early ‘90’s, but they really haven’t changed much in years so this should be relevant. As a matter of fact, I just came in from wrenching on a friend’s 90 model (with a ’89 front end) in the garage.
Unless you ride desert-type, wide-open conditions, I don’t think I’d go for the carbon reeds and rev-plate combo. I’ve had good luck and service with the original Boyesen reeds once the stockers go.
The jetting on all of them I have owned was rich off the bottom making the engine blubbery and raspy at low-throttle settings. If yours is like this, try dropping one size on the pilot and then evaluate the performance. Fine tune with the needle clip. Once you get the jetting crisper on them you’ll be surprised how much better they run.
Buy removable strength Loctite… by the gallon. They have some heavy vibes and will scatter themselves over the countryside if given the chance.
I’ve seen the inserts in the aluminum subframe strip, the ones where the seat, sidepanels, etc., bolt on.
The engines are anvils, but like anything, proper maintenance is a must. Clean and oil the air filter religiously. I personally like Maxima FFT.
Like any Open bike, good sprockets and an O-ring chain are wise investments.
Due to the vibes, any crud that gets into any moving part (kickstarter knuckle, brake pivot, etc.), will help wear it out fast if not cleaned.
Keep an eye on the spokes during break-in.
Footpeg mounts and the aluminum rear muffler bracket are also prone to failure.
They’re really great bikes, just pay attention to it and keep a log of what seems to be regular attention areas and you’ll enjoy it for years.
Hope it helps!
:)