I have had MANY CR500's and have been on my street legal KX500 for a little over a year now and from expereince can say:
The KIPS valve 500cc Kawasaki motor is an AWESOME woods bike!! Wanna idle thru the tightest, narlyest, greasiest crap known to man kind and then real in ANYTHING short of a Dodge Viper from corner to corner? Put on a flywheel weight and you will be SHOCKED!! Wanna DOMINATE in the whoops? Pin it and cut the tops off the suckers!! Wanna putt? hows all day long without fouling a plug sound! Wanna FLY, how's tooling along the highway at 75 mph and twisting the grip to bring the front end up sound? Wanna freshen the motor up at 6 thousand miles on the stock piston? Hows $150 for a NEW top end job sound!
Wanna know the down side of BIG BORE RIDING - THEY EAT TIRES!! But hey, everything has its price :) :)
Woodsy