‘00 KX250 Swap Items

[KDXGarage]

Do yourself a huge favor and start making some big changes to the base valve now. They will beat you to death.

[Bz1hx]

Do yourself a huge favor and start making some big changes to the base valve now. They will beat you to death.

Point taken. From what I’ve read, seems like taking out 7 of the 24’s in the base valve is a good starting point? Do they need to be completely removed and nothing put in their place? Removed and washer added to the bottom of the shim stack? Or just relocated to the bottom of the shim stack. Forgive my ignorance

[KDXGarage]

I would focus on the high speed portion. You might want to take 1 or 2 of the low speed 24's out or move them underneath.

[Bz1hx]

Hello all,

I’m reviving this thread. I’ve ridden the bike quite a bit now with the new forks. Overall, it was worth the effort for the swap. I think I’m pretty happy with the low speed compression damping. On single track and flowy dirt atv trails I have no complaints on how the suspension feels. The high speed compression damping is killing me though. Especially on rough rocky sections it’s very harsh. I rode a buddy’s bike and now I know what I’m missing. It was so plushy it felt like cheating.

So, I think it’s time to get into the mid valve. I know I probably won’t be able to achieve what a modern bike can do, but I’m willing to give it a go. I’ve done some searching and it sounds like I need to add some float by replacing the o-ring with a spring (where to obtain said spring, I’m not sure). And/or rearrange some shims. Any advice would be helpful here.

[Bz1hx]

After lots of digging it seems that KYB used an 8mm check spring in the midvalve on some models. My year of KYB46U forks should have an o-ring rather than a spring. The closest thing I can find is the below spring without having to pay for international shipping.

https://mx-tech.com/check-valve-spring-9-4mm-od/

[Chuck78]

Oh wow, I didn't know that about the KYB 46's mid valves for certain years.

I'd suggest softening up the mid valve as much as possible without adding too much float (adding a lot of float is a common DIY technique, though.).
With too much float, you won't be utilizing the base valve enough. It's important to push fluid through the base valve, and a lot of mid valve float sort of bypasses that... Turning it into a fixed orifice up to certain compression velocities.

[Bz1hx]

Oh wow, I didn't know that about the KYB 46's mid valves for certain years.

I'd suggest softening up the mid valve as much as possible without adding too much float (adding a lot of float is a common DIY technique, though.).
With too much float, you won't be utilizing the base valve enough. It's important to push fluid through the base valve, and a lot of mid valve float sort of bypasses that... Turning it into a fixed orifice up to certain compression velocities.

Yep, supposedly there’s an o-ring instead of a check spring. So, hypothetically, there’s currently no float. My plan is to pull it apart, see what I’m working with. Remove the o-ring and install a spring. I’ll probably try and re-order the existing shims to give it about 0.5mm of float, and possibly add a bleed shim and crossover shim. Any thoughts on the spring above? I think it’ll work but who knows.

I think the fork springs are correct. Stock they’re 0.43kg/mm and I weigh about 215 with all my gear.

[KDXGarage]

I once did a swap for a friend with 2000 KX125 forks. A tuner in the UK (mog) told me to go with 0.4 mm of float. I swapped in the spring instead of the o-ring.

I got the springs from Race Tech. Their Gold Valve paperwork showed to do the spring swap.

[Bz1hx]

I once did a swap for a friend with 2000 KX125 forks. A tuner in the UK (mog) told me to go with 0.4 mm of float. I swapped in the spring instead of the o-ring.

I got the springs from Race Tech. Their Gold Valve paperwork showed to do the spring swap.

I might have to call them because I can’t find it on their website. It also appears that gold valves are only available for the base valve. These are old forks so I wouldn’t be surprised if the support for them has diminished.

EDIT: Called Racetech. They do have check springs. Part number FPCS-01 is an 8mm spring, which should fit the bill. I’ll report back once I get the springs and take apart the forks.

[KDXGarage]

Cool.

Look to see if I posted what stack I went with back then (20 years, ha ha). I think it is the same base valve and valving for both KX125 and KX250 that year, if my memory is correct.