250 yz shim stack

[f_red]

Hi i am from france and i'm new on this forum.
I have a question to tune my kayaba fork. This fork is made for mx ride but i want to set it for a woods use. My compression shims stack is actually:
2*22*0.1
1*20*0.1
1*18*0.1
1*16*0.1
1*14*0.1
1*11*0.3 (down)

Do you think that it will be good if i remove on of the two 22?
If not you can suggest me an other shim stack...
Thank you for your help.

 

[steve125]

I would start with pulling 1 of the 22's out and put an 8 or 9 under the 11. It would be best to change the 11 to a 0.1 in thickness, the 8 or 9 wont matter(thickness), like any last shim. That and 1 step softer fork springs should be a good start.

 

[Miedosoracing]

That isn't stock, that isn't set up for motocross either. You don't want it any softer than that. That is sitting in midstroke for sure. You need to add a couple 22.1's You need 3 to 4 of them to keep your bike up. Anyone else agree? That is about as soft as it gets. I would say almost needing to get .15's and replace all those 20.1 on down.

 

[KTM-Lew]

Miedoso.......ahhhhh.......forget it.....

 

[steve125]

I agree with miedoso, thats a soft stack to begin with. I just figured he has ridden the bike, and wants it very soft for the woods. I would think the std stack for a 250 would have at least 7-9 22x1's?

 

[Miedosoracing]

Miedoso.......ahhhhh.......forget it.....

Go ahead and say it.

 

[Miedosoracing]

I agree with miedoso, thats a soft stack to begin with. I just figured he has ridden the bike, and wants it very soft for the woods. I would think the std stack for a 250 would have at least 7-9 22x1's?

Yeah, I figured he rode it as well, and thought it felt stiff, but what someone thinks they feel, and what that stack is saying, is just not matching. I wonder if stiffer springs have been put in, or is it the harshness that he is feeling from the bike hitting bumps while he is mid stroke??

 

[Rcannon]

How woudl that stack best be modified for motocross????

 

[russ17]

Man I would have to wonder what year YZ this is. Must be awhile back as they used 24's for face shims on a stock piston. The guy might have aftermarket pistons.
If this is the case, I would be looking into the size of the porting as this very well could be a MX setting.

Russ

 

[Miedosoracing]

you guys ever notice, that some people post a question, and never come back. I am not saying he won't be back to see what was given, but I always thought it was funny that some don't.
Oh, and Cannon, I will email you. i have been busy. We can go over your shims.

 

[stimps]

YZ250- 2000 model. Got the forks stripped down as we speak, not taken cartridge apart only base valve. Almost entirely MX raced but on some quite rough chopped up tracks.
Std spring 0.43, weigh I guess 190lb. Intermediate rider. Any suggestions on stack to improve for the specs given above. Want to improve the action on the braking bumps coming into corners. Deflects and transmits a bit too much shock at present. Don't want a woods set-up if it means It will bottom out on the bigger stuff. Is this possible. cheers.
Current stack
24.1 (Qty 12)
22.15
20.15
18.15
16.15
14.1
14.1
11.25
18.5
18.5
18.5
11.25
24.1

Top too bottom on the whole stack. Any help is greatly appreciated.

 

[Miedosoracing]

I will let the other suspension guys answer the whole stack, but my favorite starting point is to eliminate all but 4 24.1s. Thus, you will probably need to stiffen up towards the middle of the stack. Like I said, they can answer that part. I shim mine WWWAAAY different than any of the big guys.

 

[KTM-Lew]

I would replace all the .15's with .10's. Then you have something we can work with. Miedoso is trying to be "different" for some reason all his own???? Maybe it will make him rich but I doubt it.....

 

[stimps]

Should I still stick with the big stack(12) 24.1 on the top. thanks for all the advice.

 

[KTM-Lew]

stimps

You may get away with pulling a couple but I wouldn't go too far. Changing the .15's to .10's will decrease the damping curve across the entire range but has more effect on the high-speed. You can pull the base-valves at the track by flipping the bike over and popping them loose with an impact driver. Do both sides at the track in 15 minutes! They will self bleed but don't just take off and hit a big triple right after. Ride a couple of easy laps first.

 

[russ17]

Stimps,
I would start with Lews suggestion first. then proceed to elliminate some of the 24mm that way you learn and feel the changes.
There is also a midvalve issue you will need to have taken care of. On the earlier KYB's, the midvalve comp shims are prone to distortion and needs to be addressed.

 

[Rcannon]

you guys ever notice, that some people post a question, and never come back. I am not saying he won't be back to see what was given, but I always thought it was funny that some don't.
Oh, and Cannon, I will email you. i have been busy. We can go over your shims.

Chad, no problem. I noticed Forslyk is on page 68 of the newest dirt bike magazine. I can imagine this might create some chaos....

I appreciate all of you guys that are not afraid of helping people learn al bit about valving.

Somehow the topic is supposed to remain a secret. A person can search the internet and find plans to build their own automobile. Ford and GM dont appear afraid.

You can also get plans for a DIYat-home vasectomy. Doctors appear to be doing rather well.

 

[f_red]

thank you guys for your answers!
This 250 yz is from 1994 and the spring is stock. This is the first time that i try to modify a stack and i'll try to explain you what i want. Woods bike are soft on small shock, when you ride on a 5 or 6 cm rocks you don't feel it in your arms and thats what i want to do on this fork. But my problem is for translating what i want on stack. Can you explain me the influence of each shim? For me, if the fork goes slowly in compression, only the first shim (contacting piston) is deformed? that's why i want to remove one of the 22*0.1. Am i ok?

 

[WWR]

f_red,
the larger shims effect more of the low-speed damping (big jumps, bottoming resistance) while the small shims effect the high speed (fast, chattery bumps). The progression, taper, and volume of the shimstack all effect the entire range, but some more than others as listed in my first sentance. The "speed" referred to is the speed at which the forks travel, not how far they travel. In other words, at 60mph a 3 inch bump will cause the forks to reach a higher damping speed than, say, a 3 foot jump will at 5mph. The forks will go through their travel farther, but at a slower speed.

Hope this helps.

 

[Rcannon]

May I offer my humble opinion. Do exactly what Chad said to do with your forks. He may do things a bit different, but damn, it really works.

I followed the instructions in this thread and applied them to my 97 yz 250. The difference is nothing short of amazing. My forks felt excellent in all conditions.

I think this fork business just might make him rich. He knows what he is doing.

My forks were previously revalved by Factory Connection. Chads instructions in this thread blows them away.

 

[f_red]

Thank you for answers, in france it's really hard to find information about suspension tunning!
If i understand what wwr say, my fork can be optimised for one type of bumps run at a given speed. If i'am out of this situation, my settings won't be optimal? or can i be optimal for a whole range of riding conditions? (differents size of bumps run at different speeds)?
excuse me for my english....

 

[Miedosoracing]

red the reason most tuners are going with either different thickness shims at the middle, or end, and why they are chosing 2 stage and now even 3 stage stacks are to get optimal everywhere. Everyone wants a plush but not too soft first hit, but don't want to blow through the stack either. Now, that being said, it is hard to get one set for everything. Only people who have dealt with all these shimming needs will know what to do, and they won't give all the info out. So, since you are focusing on offroad, and not motocross, you can lean towards that end of things. And still make the last part of your stroke stiff enough so it won't slam down on jumps. Sounds like you only want softness, so make it so the shims bend down easy. basically what they said on this topic, go thinner on everything to do that. Even though I don't completely agree, it will do what they said. good luck

 

[renes]

I had a 94 YZ250 and my stack was alot different. This is the stock 94 YZ250 stack in North America.

6-22x0.1
1-20x0.1
1-19x0.1
1-18x0.1
1-16x0.1
1-14x0.1
1-11x0.25

Now, I weigh about 200 Ibs and also ride in the woods and I did nothing on the valve stack. The stock bike came with only 0.39 springs. Way way too light for a heavier rider. I moved upto 0.43 springs and it made a HUGE difference. The reason you are having such a problem right now is you are too low in the stroke of your fork. The stiffer springs will make the front end sit up higher and you will have 2/3s of the stroke to move in, not 1/2 of the stroke. I would definitely get the right springs first before you change anything in the stack. The stack you posted was a really weak stack. I bet once you change the springs you will actually add more shims. I'm surprised nobody here has not mensioned replacing the springs.

 

[KTM-Lew]

renes

You have nailed it on the head! Somehow we all went off on the wrong track. I wondered about the (2) shims on the face too?

Fred

What do you weigh?

 

[renes]

I think he said he was 190. I'm 200 and thought my setup was a bit soft and I like a soft setting while in the woods. So 0.43 might be good for him too. Or maybe a 0.42 and a 0.43.

After installing the springs I found that the bike would just "float" over rough and rocky sections. It was awesome. You might also find that your rear spring is very light too. I had to use almost the entire pre-load on the shock to get 100 mm of race sag. Not good.

Now if only I could get my 99 YZ250's suspension to feel as nice as my 94's did.