Changing your WR's cam timing to YZ Timing
Works on 98'-02' WR250F/400/426
The WR 250F/400/426 has been mellowed in comparison to the YZ 250F/400/426. You can change the timing to YZ specs and increase the mid rev punch and build RPM's quicker.
Remove the seat and fuel tank. In the manual it says to remove the radiators, you don't need to remove them. Instead remove the upper engine brackets. This will give you enough room to slide the Cylinder head cover out. Now remove the Cylinder head cover.
Remove the timing hole plugs and turn the engine until "I" is in the center of the small plug hole. At Top Dead Center the cams will be facing away from each other. The exhaust cams will have punch marks at 9:00, 12:00 and 3:00. The intake cam will have punch marks at 9:00, 12:00 and 3:00.
Remove the cam chain tensioner. Use a screwdriver to tighten the screw inside the tensioner until it locks. Then in a criss cross pattern remove the cam chain tensioner
Loosen the cam cap bolts in a criss cross pattern and remove the cam cap. (There's a bearing retainer in the cam cap, be sure not to drop it into the motor.)
Turn the exhaust cam one tooth clockwise. The timing mark on the exhaust cam will now be at 1:00.
Reinstall the cam caps and torque to 7.2-ft. lb., then reinstall the cam chain tensioner and unlock it.