I used to own a '98 and it was an excellent motorcycle(miss it sometimes!) Stock settings on the '98 KX250 are actually pretty good for trail riding.
If it is completely stock, you should look into .42 or .43 straight rate front springs. Oil level should be about 95mm-100mm from the top. Experiment with running that higher oil level with lower compression clicker settings and a couple more clicks of rebound (slow it down) from stock.
The rear stock spring (maligned for moto) is progressive as well, but I found it worked extremely for trail riding (especially small acceleration bumps). Just dial in about 3 3/4 inch of preload, up the compression a couple clicks from stock as well as the rebound (slow it down).
If you plan to moto, change the rear spring to a straight rate 5.2 or 5.3 It offers better balance and more consistent jumping manners.
Also, there is a great offroad tuning guide offered on Jeremy's web site
www.mx-tech.com
Regards,
Ted
'01 KX250
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Ted
2001 KX250