No nitrogen in the forks?
That's all I have ever used.
Then again I have never tried to raise or lower my bike by fork pressure, I have only put in the recommended amount.
The last bike I did this with was a 78 rm250 and if I'm not mistaken the manual recommended it.
Newer forks don't use it but I could swear the older style used it.
Then again it's been 30+ years and my memory could be doinked.
Why no nitrogen?
Guess we could eleborate on this more..
#1 we need to know the year of his KX250..
many of the motocross bikes from the 70's and early 80's were designed to have a "shot" of air in the forks.. (few of my old Huskys want it)
Anything Modern.. say.. 84 and up (just wrote down first number that came to mind)... uses ambiant air pressure..
Before you go for a ride... race.. etc. you TOP OUT the forks... release the bleeders... and screw back in.. once suspension settles, you have some pressure due to compression.. and.. deffinatly once you start riding.. heat build.. which causes more pressure...
some FAST guys I know.. actually have to release pressure in the middle of the race, because they will blow out seals, just from heat and pressure buildup..
If your having to put a shot of Nitro or air in your forks to make them ride how you want.. (stiffer, with less bottoming) you need to add more oil to get a differant "air spring" volume...
If you just want to raise the bike up... you need differant fork springs. / preload on said spring.
Then again.. I could be wrong also