[Duster]

Now some guys have had zero electrical problems and 100% good experience.

But if you buy a used one, I'd say the chances are high that you are buying a buggy trade-in. But I can guide you through any troubles.

My advice for good KFX450R service is...

Download factory service manual from internet (free)
Buy 2 multimeters, 1 digital autoranging, 1 analog
($45 for both at Sears or Walmart)
Unhook every connector and put in dielectric grease.
Buy the throttle sensor setting adapter and hook it up inline
Use digital multimeter to check TPS periodically
Never install higher rated fuse in place of a blown fuse... find the problem
Exercise common sense if you use pressure washers

Use very robust synthetic oil... change when it looks dirty in sight glass
(15w50 Mobil 1 in summer, 10w40 Mobil 1 motorcycle in winter... or Amsoil equivalent)
Service air filter religiously when needed.
Don't use K&N filters unless covered with outerwear and used in desert (large particulates)
Disassemble and grease suspension pivot points periodically
Don't install fancy lightweight sprockets ever
Check chain slack and sprocket bolts regularly
Buy a Moose Poly case saver in case anything ever goes wrong with the chain
Put good skids under the aluminum frame

Remember this EFI system has no ability to adjust for mods