Like you I brought a 1997 kx250 that had a blown crank, Broken rod in forks, rust, exhaust held on with number 8 wire....... basicly the guy sold it to me and said it used to go hunnits as g. So while recovering from nearly losing my foot 2 years ago I completely rebuilt every single part of this bike over 8 months and now I ride / race it 3x a week. I know this bike inside out and heres what I found.
Cylinder powervalves - getting hard to find / obsolete parts the toothed gears wear out. but there is a person on ebay who can make them.
Kickstart shaft and parts - Can be hard to find as parts are obsolete
indent spring on the main selector fork is weak and needs to have a stronger spring fitted for better shifting between gears.
linkage and shock bearings. shock bearings don't last long so keep a stock pile.
get a good set of stainless spokes and relace those wheels I would invest in a good set of excel rims also.
The older kxs powerband can be a bit like a lightswitch so even for motocross I would recommend a flywheel weight.
Yes it will cost money. Yes it will take time. But when you come out on the other side you will have a really competitive bike that always sticks out at race day ( The old kx sounds amazing)
