1997 KX125 fork needs damping help.

Questions and comments about converting to beefier forks..
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SoCal Headgrinder
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1997 KX125 fork needs damping help.

Post by SoCal Headgrinder »

Help!  I put 1997 KX125 forks on my 220.  The shop I used is well known, friendly and does good work.  He sounded confident when I dropped them off but the first configuration he gave me was unrideable.  We've gone back and forth 4 times and they are now rideable but no where near compair to my 1995 kx250 which is amaizing.  So I know the older forks can be made to work.  Unfortunately the guy that did the KX passed away some time ago.

I am 235lbs and used to be fast but mostly ride at just a quick pace these days.

What I know of the current set up.

1 inch lowered internally
.46 custom springs set at 6mm preload
5wt oil
120mm oil height
2 face shims and a 2 stage base stack
Midvalve o-ring removed replaced with spring.
Compression clicker all the way out.

The rear shock works well and the free sag is 35mm and rider sag at 105

So the bike is becoming fun to ride again but the main problem is over small square edged bumps.  Like the acceleration/braking type.  I would also like to see the clicker not all the way out.

Anyone have any advice as what to change/focus on next?
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Re: 1997 KX125 fork needs damping help.

Post by SS109 »

Sadly, I don't know enough about changing shim stacks to help. I do know those forks can be made to work very well as I had a set (redone by Donnie at ZR1 Suspension in Tucson) on my '90 KDX that were awesome. I also know that having any clicker to the fully closed or open position means something isn't right and some changes/repairs or a revalve is in order.

Personally, I would start with reducing the oil height to the minimum recommended as you can always add to it later if needed. You could also try reducing your preload on the spring to 0 and see if that helps.

Hopefully someone more experienced with valving comes along to give you some help in that department.
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Re: 1997 KX125 fork needs damping help.

Post by KDXGarage »

Did he do anything to the MX midvalve?

The answer is in the valving. Everything else seems fine to me.
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Re: 1997 KX125 fork needs damping help.

Post by Slick_Nick »

Your compression clicker is all the way out??? That's your issue right there!

You've got no hold up anymore. Your forks are using 3/4 of their travel over the smallest bumps, and when you hit something square edged, you're into the bottoming cone, which is very abrupt and harsh.

Turn those clickers all the way in, and start at say, 4 clicks out on compression. Start with the rebound around 12 clicks out. Were the '97 forks bladder forks? I've got '95's on mine and even after a few woods revalves, I'm coming back closer and closer to stock KX125 valving to make them compliant. I know my '95's were the first year of the midvalve, but still had no bladder.

The oil height in the open cartridge forks has more to do with bottoming resistance than it does any sort of trail compliance. Stick with stock.
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Re: 1997 KX125 fork needs damping help.

Post by SoCal Headgrinder »

Slick_Nick wrote: 09:19 am Nov 18 2021 Your compression clicker is all the way out??? That's your issue right there!

Turn those clickers all the way in, and start at say, 4 clicks out on compression. Start with the rebound around 12 clicks out.
The 97 forks are open with no bladder.

If I turn the compression clickers in it gets worse and the bike gets hard to ride.

From what I have read it seems that the midvalve is where the issue may be.  Does anyone have a recommended amount of float or maybe shim stack?

I am feeling pretty down and that I made a mistake doing the swap.
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Re: 1997 KX125 fork needs damping help.

Post by Slick_Nick »

Compression clickers are only have the story. What’s your rebound at? If the forks are packing you’ll have a super harsh feel.

With your compression clickers all the way out, the base valve is essentially doing nothing. You’re bypassing it, and putting all of the compression stroke onto the midvalve. It’s not designed to work that way, I think you are blowing through the stroke. The midvalve has a limited damping window, it’s designed to be cumulative. If you’ve eliminated base valve damping with the clickers out you’ve essentially spoiled the entire compression circuit.

Those springs are also super soft for you at 235lbs. Stock KX125 is .43 I believe, **** I’m 175 and I run .48’s for woods. You’re always better off having softer valving with stiffer springs for a woods bike in my experience.
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Re: 1997 KX125 fork needs damping help.

Post by SoCal Headgrinder »

Slick_Nick wrote: 03:07 pm Nov 18 2021 With your compression clickers all the way out, the base valve is essentially doing nothing. You’re bypassing it, and putting all of the compression stroke onto the midvalve. It’s not designed to work that way, I think you are blowing through the stroke. The midvalve has a limited damping window, it’s designed to be cumulative. If you’ve eliminated base valve damping with the clickers out you’ve essentially spoiled the entire compression circuit.

Those springs are also super soft for you at 235lbs. Stock KX125 is .43 I believe, **** I’m 175 and I run .48’s for woods. You’re always better off having softer valving with stiffer springs for a woods bike in my experience.
The rebound is currently at 14 clicks out.

I get that if the compression clickers are all the way out it by-passes the base valve but if I put any clicks into it the damping the forks become harsh on everything and not just the small sharpe edge stuff.  So how do I "unspoil the whole damping circuit"?

It was years ago but I have ridden a stock suspended KX125 (.43) and yes the springs were a little soft and I could bottom them out but it didn't have the same damping issue as these do. 

With the current springs I am not bottoming out and the rider sag doesn't seem excessive.
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Re: 1997 KX125 fork needs damping help.

Post by SoCal Headgrinder »

Is there any where I can find what the stock base and midvalve shim stacks are? Maybe I should just find someone to put it all back to stock.
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Re: 1997 KX125 fork needs damping help.

Post by Slick_Nick »

ValvingLogic might have the stock stacks, but I suspect those forks are too old.

How did you install the forks in the clamps? If they’re not properly torqued, or centred, they will bind big time. Did you install and torque the top clamp before installing the fork legs?
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Re: 1997 KX125 fork needs damping help.

Post by SoCal Headgrinder »

Slick_Nick wrote: 06:02 pm Nov 18 2021 ValvingLogic might have the stock stacks, but I suspect those forks are too old.

How did you install the forks in the clamps? If they’re not properly torqued, or centred, they will bind big time. Did you install and torque the top clamp before installing the fork legs?
Thanks so much for trying to help!

He looked in some spread sheet and it didn't go back that far if I remember correctly.

The fork binding was the first thing I thought of/checked.  When I first got the forks the action was so harsh/firm and just seemed to ride/bounce on top of everything.  Couldn't even hold onto the bars over anything. So I loosened and tightened everything in various orders.  One tub slides in and out nicely and the other takes just a minimal amount of twisting as you slide it in the triples.  I've had bikes that were way worse/tighter.

Over the first ride I would back the compression clickers out more and more till they were all the way out.  It was fine following my son around.  The second ride was with some buddies so the pace increased and it was so hard to ride and I got terrible arm pump.

Took it back and he removed a base shim.  Rode again and it was margenly better.  I also took 2 clicks out of the rebound.

Took it back and he removed 2 more base shims (only 2 left now).  Margenly better again.  I asked about the midvalve and he said he was pretty confident in his set up of it.

Took it back again and he lowered the oil height from 105 to 120.  This made a big difference and the forks now worked better in the whoops and most trails.  At a fast pace I can manage the arm pump and it would subside if I backed off a bit.

The forks still seemed to want the compression clickers all the way out.  But the bigger concern is that they don't seem to absorb small square edged chop. Like acceleration/braking shutter bumps.  This goes for both when I am on the throttle or coasting.  I feel each individual bump.  I have ridden the same trail on my well set up 1995 KX250 without issue.  With the stock revalved and resprung KDX forks I rarely got arm pump.

When I picked the forks up last time he made the comment that "these forks weren't that good back in the day".
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Re: 1997 KX125 fork needs damping help.

Post by KDXGarage »

Get on ThumperTalk suspension forum and read, read, read. If everything is working properly, then it is the midvalve and base valve. Just removing more and more shims may not be the best way to go.
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Re: 1997 KX125 fork needs damping help.

Post by SoCal Headgrinder »

KDXGarage wrote: 02:19 am Nov 19 2021 Get on ThumperTalk suspension forum and read, read, read. If everything is working properly, then it is the midvalve and base valve. Just removing more and more shims may not be the best way to go.

That's why I took it to a suspension shop.  In the hope that it would be close when I got it back.  The shock he did works great.  We have made progress in the forks but I fear he has lost "enthusiasm".  It seems to me that it is a midvalve issue.  I guess I was hoping someone would confirm this and know of a good baseline midvalve shim stack and float number so I can give him a suggestion or at least have a clue when I talked to him next.

The big issue for me to take over the valving work is that I would not be starting from stock and I can't seem to find what stock was. I am also buried in work and after 3 month of installing the front end and adjusting it I just want to go riding with my son. I am inclined to just put the stock front end back on because they will be soon closing the mountain riding areas for the winter.
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Re: 1997 KX125 fork needs damping help.

Post by KDXGarage »

Is 235 your weight in full gear or do you ride nekkid??
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Re: 1997 KX125 fork needs damping help.

Post by Slick_Nick »

Lets back it up a bit. Basically, the KX125 forks in their stock form, sprung for your weight, work pretty good in the woods. The 90's motocross valving is very similar to the woods valving on modern bikes, so if you bolted on some stock KX125 forks, you'd be happy. I can attest to this, I rode my '95's completey stock a few times before modifying. The KDX is a much heavier bike than what those forks were designed for, remember. In addition to that, you are a heavy fella, and you've got an oversized tank. That's asking a lot of those forks without some serious springs in there. .46's are way too soft in my opinion.

With this in mind, after your comment that your tuner took more and more shims out of the base stack, I believe your problem continues to be that you do not have enough damping, rather than too much. You're riding so low in the stroke of the fork over small stuff, that when you finally do hit a square edged bump, there's hardly any travel left, you're into the bottoming cone on the cartridge, and you're getting a super harsh feel.

Have someone video you from the side while you hit some chop. Put a zip tie around one of the fork legs, go over some SMALL chop and see how much travel you're using, and report back.
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Re: 1997 KX125 fork needs damping help.

Post by KDXGarage »

Yes, the zip tie is a great idea.

It is the same base valve as 1997 KX250 if you ever see anyone posting about those forks.
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Re: 1997 KX125 fork needs damping help.

Post by SoCal Headgrinder »

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Re: 1997 KX125 fork needs damping help.

Post by SoCal Headgrinder »

Thanks for the input KDXGarage and Slick_Nick! Suspension guy got back to me and says the same thing.

"Have someone watch you ride the section you are struggling with and/or film it to verify where you are in the stroke. Add compression if you are starting out low in the stroke."
Slick_Nick wrote: 10:06 am Nov 19 2021 Have someone video you from the side while you hit some chop. Put a zip tie around one of the fork legs, go over some SMALL chop and see how much travel you're using, and report back.
We are going on a family ride so I don't know if I will be able to have anyone film in the harder faster stuff but I can do a solo loop and check and reset a zip tie on the fork for each type of section. I will also try adding compression clickers as well. Do you think I should just go back to 14 clicks out and start again from there or should I just add one or 2 clicks in at a time and try it?
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Re: 1997 KX125 fork needs damping help.

Post by KDXGarage »

How many runs do you want to make? I would try 12 out, then six, then none. Make big changes.
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Re: 1997 KX125 fork needs damping help.

Post by Slick_Nick »

Yes make big changes. Do one run with them all the way out. I wanna see how stiff they are with no damping.

Only adjust compression on the fork for this test. Don’t add any other variables. Once we see if you’re in the ballpark, we can then fine tune with rebound etc, however, your rebound clickers should be set to 12-14 out for those tests, which is pretty quick, but will ensure we are measuring the changes on the compression side without the fork packing.

Just to clarify, the compression clickers are on the BOTTOM of those forks, rebound is on the top.
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Re: 1997 KX125 fork needs damping help.

Post by SoCal Headgrinder »

Yes the compression clicker is the one on the bottom on these forks. Currently the compression clickers are all the way out and have been for the last 3 rides. The rebound (top of the fork) is currently at 12 clicks out.

I'll go for a ride. Then I'll turn the compression clickers in (firmer) 6 clicks and go for another ride. I'll also stop between sections/terrain type and measure were the zip tip is showing what the maximum travel was.
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