I have a 2000 400 EX ...when properly maintained they are bullet proof..with a few simple mods they make tons of power ..but like any other quad, if not taken care of, they can be real junk boxes.
when looking at them, check everything you normally would, chain and sprockets, tie rods and ends, steering stem..wheel bearings and stuff like that...pay attention to the rear on these..the carriers are suspect if its been ridden hard and not had the bearings serviced..the bearing wear the carrier out and it needs to be replaced....a new carrier with bearings can be had for like $100.00 in the aftermarket.
The engines are very strong, but if its been neglected, can be expensive to fix.....you could easily spend $600.00 on a top end if its whooped....listen for any noise in the valve train...some light taping is normal, but anything more could be as easy as a valve adjustment or as bad as a bad cam chain or tensioner ..when its running look for any smoke.....there should be NONE.....
There are plenty of them out there as they are very popular, so take your time and find a good one.......around here you can pick up a nice 2005 or above for about $2000-$2300
I myself prefer stock unmolested bikes.....I can screw it up myself, I dont need to previous owner to do it for me..if its already "modded out" make sure it was done right....there lots of people with tools who should not have them..
