I have a DRZ250 with a 1997 RMX250 conventional fork that came with it when i bought it. I rode it and find it a bit too soft. wanted to upgrade it to USD fork. but concern with the money involved and time.
Any other option to make the RMX fork stiffer. so far I have max out the oil level and using a 15wt oil, compression and rebound clicker fully CW.

Maaybe changing spring is my next cheaper option than a fork swap.
difficult to find rmx spring, anyone know of other compatible spring that i can use in the rmx fork? thanks

First of all, how much do you weigh? You need to obtain the correct rate springs for your weight before you do anything else to the forks. You should be using a 5wt oil, maybe 7wt max. Any higher and the shims in the valve stack will not deflect when their supposed to, making the ride harsh. When you say "max out" the oil level, what does this mean? There should always be an air gap.

Anyways, a little research shows that there are several bikes that use the same size fork springs (diameter and length) as the RMX. Here's the list:
2002 KTM 520 MXC
2002 KTM 520 EXC
2002 KTM 400 MXC
2002 KTM 400 EXC
2002 KTM 300 EXC
2002 KTM 250 EXC
2002 KTM 200 MXC
2002 KTM 200 EXC
2001 KTM 520 SX
2001 KTM 520 MXC
2001 KTM 520 EXC
2001 KTM 400 SX
2001 KTM 400 MXC
2001 KTM 400 LC4
2001 KTM 400 EXC
2001 KTM 380 SX
2001 KTM 380 MXC
2001 KTM 380 EXC
2001 KTM 300 EXC
2001 KTM 250 SX
2001 KTM 250 EXC
2001 KTM 200 MXC
2001 KTM 200 EXC
2000 KTM 520 SX
2000 KTM 520 EXC
2000 KTM 400 SXC
2000 KTM 400 SX
2000 KTM 400 EXC
2000 KTM 380 SX
2000 KTM 380 MXC
2000 KTM 380 EXC
2000 KTM 300 EXC
2000 KTM 250 SX
2000 KTM 250 EXC
2000 KTM 200 MXC
2000 KTM 200 EXC
1999 KTM 200 MXC
1999 KTM 200 EXC
1999 ATK 605 CC
1999 ATK 250 LQ
1998 Suzuki RMX250
1998 KTM 200 MXC
1998 KTM 200 EXC
1997 Suzuki RMX250
1996 Suzuki RMX250
1996 KTM 550 MXC
1996 KTM 300 EXC
1996 KTM 250 SX
1996 KTM 250 EXC
1995 KTM 550 MXC
1995 KTM 440 MXC
1995 KTM 440 EXC
1995 KTM 300 EXC
1995 KTM 250 SX
1995 KTM 250 EXC
1994 Honda CR500R
1994 Honda CR250R
1993 Kawasaki KX500
1993 Honda CR500R
1993 Honda CR250R
1993 Honda CR125R
1992 Kawasaki KX500
1992 Kawasaki KX125
1992 Honda CR500R
1992 Honda CR250R
1992 Honda CR125R
1991 Kawasaki KX500
1991 Kawasaki KX125
1989 Kawasaki KX500
1989 Kawasaki KX125

You can use the online database on Racetech.com to find what the stock spring rates are for each of these bikes, if you are looking for cheap "take-offs" from the salvage yard or something. The stock springs in your RMX forks are .41 kg/mm, which is too light for anyone over 160-170 lbs.

Hi, thank you for the great infor. I weight 65kg without load + 10kg my load.
i consider myself a aggressive rider and pushed my drz250 further after the keihin FRC carb swap. found that the front and rear shock is not good enough to be riding safe at that speed. rear bottom out too.
I am using 15wt oil and max oil height according to the manual allows. thinking of buying a set of racetech .44kg/mm fork spring. what do you think? thanks.

Holy crap, are you using your DRZ for supercross or something? You are about the right weight for the stock springs, but if you are bottoming out frequently and violently, then you need a revalve or stiffer springs (or both). You do want to occasionally bottom out though. Anyways, the .44 rate would be a good place to start. You will probably be able to go back to a lighter fork oil afterwards.

With stiffer fork springs, you might find the bike unbalanced with the stock rear spring. You can try cranking up the preload a bit if you haven't already. It's not too difficult with the battery or carb out of the bike. That spring "should" be firm enough for your weight. If you find it bottoming too much after cranking up the preload, then you might want to look into a revalve.

Thanks alot OhioPT for your advise. I dont do SX or MX with it of course. but I do high speed trial and I dont slow down on deep ruts at 80km/hr, tats the problem. Haha... do you happened to know the stock spring rate for the drz250? i have got the service manual, but it didnt indicate the spring rate. thanks.

I just searched through the thread and found out the stock DRZ250 rear is 5.8kg/mm and the front is .39kg/mm. i will just try out the front to a .44kg/mm first and rebuilt the rear shock with more spring preload.

I dont know about the fork brace i hear it helps
i installed a set of rm 250 usd forks money well spent
the rear shock will need some work to work with the forks