99 kx250 fork problems on kdx

Questions and comments about converting to beefier forks..
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actmobmar
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99 kx250 fork problems on kdx

Post by actmobmar »

i'm going to try and set these up one more time, i ended up giving the bike to my son(175 lbs, 5'8), and i got a cr250. anyway, i have 1" risers on the bike and forks slid up 1" in the clamps to make up the difference in fork length.also set the rear sag to 3.5". the bike doesn't ride rite, it seems like the rear suspension is moving, but front isn't. a buddy of mine pushed down on the bike on the forward part of the seat by the tank, and only the rear suspension moves, no movement in the front, yet on his ktm the whole bike moves?? trying to figure out how to proceed, i changed the fork oil to amsoil lite 5, didn't help. now i'm wondering about the springs if they are correct, is there any way to pull it apart and id what the springs are? also, if you hold the front brake and push the forks down they don't always return to the same spot. ok guys, what should i do to try and fix this?
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Re: 99 kx250 fork problems on kdx

Post by Slick_Nick »

Sounds to me like you've got some severe stiction going on! Loosen everything up, axle, triple clamps, etc. With the bike on a stand, start by torquing everything to do with the wheel, then move up to the triple clamps. What did you have them torqued to before? Those bolts usually aren't very tight at all. 18 foot pounds if I recall.
'00 KDX 220R
actmobmar
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Re: 99 kx250 fork problems on kdx

Post by actmobmar »

its not binding, just pulled the springs on the bike and the forks slide freely through there range. thanks though.
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99 kx250 fork problems on kdx

Post by actmobmar »

I got a fork apart appears to be a rubber part which I assume is the bladder. There is a large white Teflon ring which I assume is what is left out to eliminate the function of the bladder. Iso there anything I should do to the upper and lower valves
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Re: 99 kx250 fork problems on kdx

Post by Tedh98 »

Do you know when the last time the bushings were replaced?
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Re: 99 kx250 fork problems on kdx

Post by actmobmar »

that i don't know, front end feels tight, no clicking or play. i have one fork totally apart and there is no play in the tubes. i did order a complete bushing and seal kit. as far as the springs, i read somewhere that the kx125 springs fit, but yet they are .38 instead of .42. would that help to get the front and rear to match? also, what can i do to modify the valves to soften the suspension? i read somewhere about leaving the white seal ring off by the bladder, and it supposedly softens up the suspension?
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Re: 99 kx250 fork problems on kdx

Post by Tedh98 »

Unless you are super fast in the woods, you will need to do more than disable the bladder to make mx forks work well in the woods. Lots of info on TT about doing that to those style forks.
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Re: 99 kx250 fork problems on kdx

Post by actmobmar »

i ordered the racetech gold valves for them, still need to figure out springs, i would've liked to get .40 but apparently they don't make them, so i'll have to go to .42
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Re: 99 kx250 fork problems on kdx

Post by Tedh98 »

.40 springs seem awfully light for a bike as heavy as a KDX and a 175 lb rider.

Before you start buying springs, first figure out what you have in there. It doesn't cost or take much to do that: spring tester

What are your front sag measurements?
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Re: 99 kx250 fork problems on kdx

Post by Tedh98 »

actmobmar wrote: i did order a complete bushing and seal kit. as far as the springs, i read somewhere that the kx125 springs fit, but yet they are .38 instead of .42.
Be careful of cheap seals, they will add a lot of stiction. OEM would be better and SKF is supposedly the best.

When I had that model of forks on my bike, I had it that the KX 125 came with .44 springs and the KX 250 came with .46 or .48 springs. But that was many years ago so I may be wrong. I do know that the KX never came with anything as light as .38 from the factory.
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Re: 99 kx250 fork problems on kdx

Post by actmobmar »

Kx125 came with .40 and up, I just figured out a way to get .40. Racetech recommended. 40 but they are discontinued, they did say they could give me a .36 and .44 and it would work the same? ?
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Re: 99 kx250 fork problems on kdx

Post by actmobmar »

Kx250 came 42 or 43, 125 was 40 or 41
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Re: 99 kx250 fork problems on kdx

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Re: 99 kx250 fork problems on kdx

Post by Tedh98 »

That chart doesn't make a lot of sense to me. It is saying that there is no difference, in terms of spring rate, between a 145 lb rider and a 180 lb rider. And is the rider weight with gear or no gear?

And why are you wanting .40's if that chart is saying .43's?

If it were me, I wouldn't spend any more money until I made sure those forks were in good working condition. If something is bent or worn out, putting new parts in there is a waste of time and money.

I would also figure out what springs are already in there. What if you already have .40's or .44's or whatever you are wanting to get?
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99 kx250 fork problems on kdx

Post by actmobmar »

my gut feeling is these forks have the original kx250 springs in them which don't match the kdx. i've already done runout on the fork tubes and they are straight, and the bushings look good, but i ordered new anyway. i need to look and see if there is an skf part number posted for the seal. everything i've read says the forks need to be resprung/revavlved for woods riding.
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99 kx250 fork problems on kdx

Post by actmobmar »

also, u can see with additional weight they changed the fork oil level
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99 kx250 fork problems on kdx

Post by Tedh98 »

actmobmar wrote:my gut feeling is these forks have the original kx250 springs in them which don't match the kdx.
The KDX has to be closer in weight to the 250 than the 125.
actmobmar wrote:also, u can see with additional weight they changed the fork oil level
Oil levels play a bigger role in bottoming resistance than they do when the bike is just sitting there and you push down on it.
actmobmar wrote:everything i've read says the forks need to be resprung/revavlved for woods riding.
Simply put, you spring for your weight and valve for the type of riding. Woods guys may go a little lighter in their springs than MX guys, but IIRC your main issue was that the forks just weren't moving.

If your son was 135 lbs than it would be a no brainer that he needs lighter springs. I think I asked and someone on TT asked as well, but what are your sag measurements? That will give you a better idea of what is going on than guessing and possibly buying parts you don't need.
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99 kx250 fork problems on kdx

Post by actmobmar »

problem is i have the forks totally torn apart on the bench rite now, so i can't do a sag measurement. do you know what the skf seal part number is?
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Re: 99 kx250 fork problems on kdx

Post by actmobmar »

figured i'd give an update, so hopefully this will help someone else as there isn't alot of info out there on this. i rebuilt the forks, took an hour to replace all the bushings and seals once on the bench. i eliminated the bladder seal(white teflon ring), from what i found on kx forumns this gets rid of some harshness. put .41 springs in out of a kx125(2001), and used amsoil lite 5 suspension oil. bike is now balanced, and rides like a dream. after talking to a couple of people i didn't install the gold valve kit, they felt the original valves were better. forks are set 1" up in the tripple trees, and oil level is 110 mm. my friend who is a b rider rode it yesterday as well, he rode it in the past and disliked the way the suspension worked and promptly brought the bike back. yesterday he was gone for 5 minutes on it and liked the bike now. it goes over roots and small stuff perfectly now without beating u to death, and now carves in turns.
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