YZ 125 Fork Set-Up

[lwsmithjr]

My son just recently graduated from an 80 to a 125. We bought an'01 YZ125. I rode the bike for a few months while he was finishing the racing season on the 80. After all I've read on the YZ, the forks are supposed to be some of the best off of the showroom floor. But he and I both feel the forks are extremely harsh. We replaced the springs (front and rear) to match his weight last week. I've followed the recommended settings for compression and rebound (and tweaked from there) but he feels that the front end is so harsh that if he went any faster, he would lose control. The only variable that I've left alone is the oil height. Yamaha says 135mm, MX-Tech says 120mm, Race Tech and Pro-Action both say 90mm. Anyone got any ideas? He 5'9" and weighs 140lbs. I was really hoping we would be able to live with the forks as they are for a while without a revalve.

Any suggestions would be greatly appreciated!

 

[MikeT]

I think more oil wil make the forks stiffer at the end of the stroke (compressed). If he thinks it is too harsh, I'd go with less oil which would be 135mm from the top of the tube. Try that, then try 90mm. Each extreme will give him an idea of what that modification will do and give him an idea on what feels better. Keep us updated.

 

[gbs1]

120 TO 135 MM oil range is good I personally would start with the 135 but since you are still harsh you could be dropping in the stroke a bit creating some harshness.
Try 125 mm oil height comp@ 12, RB adjustment @ 8-9 use these as a base line and fine tune your adjustments from there. adjust your oil level 10 mm at a time. Good luck

 

[lwsmithjr]

Forgot to mention that the level is currently 135mm!

 

[gbs1]

right that is why I said try 125 mm.

 

[bclapham]

who's suggested setting are you using? allthough the valving is different my 01yz250 forks also felt stiff and i am a heavier rider (it has been resprung and valved). i though the forks were a bit over stiff, in the end i backed of the rebound and added more compression to make them feel a bit softer...go figure! this probably wont work in your case but maybe worth the try....the "suggested settings" comment rang alarm bells, i see MXA printing clicker settings all the time but i have as much contemp for those numbers as i do their jetting specs!

 

[bclapham]

forgot to mention, 135mm and 2.5wt oil helped a little for me

good luck

 

[gbs1]

Bclapham, is correct you can also try his way too. But since the comp adjustment primarily controls the first 4 inch of travel, going in to far on the comp can still cause some harshness plus make the front ride higher in the turns.

By in creasing the oil level you take up the air space or increase your air spring allowing you to keep your clicker range out in the plusher range plus the higher oil will help hold the bike up. try both methods and see which suits your needs, either way you should find a happy medium.
good luck

 

[lwsmithjr]

I have looked at just about every available source for recommended settings (yes, MXA included). They all say very close to the same thing: 10 -14 compression and 10-12 rebound. I've used all of the above (all kinds of combinations!) and it just doesn't seem to make a lot of difference. As I said, the only thing I have not messed with is the oil level. It's almost as if it goes through the initial part of the stroke immediately, then at about half travel it's rock hard. Braking bumps and small to medium chop are dealing him fits. He says he feels the bike is going to toss him. I'm going to try increasing the comp. and backing out on the rebound first (quikest and easiest) and if that doesn't do it, then we will start with the oil level. Might try the 2.5 wt. too! Since it's sprung lighter now, I have to be more dependant on his feedback. I'll let you guys know. THANKS!

 

[marcusgunby]

I dont think differernt air gaps is going to fix your problem-it sounds a bit more deep rooted than that.I would get them serviced and also do a search for info on fork alignment-maybe you have the forks binding-check also the triple clamp bolt torques.

 

[bclapham]

Originally posted by lwsmithjr
It's almost as if it goes through the initial part of the stroke immediately, then at about half travel it's rock hard.

maybe youve got a build up of debris in the valves so they are not doing there job properly. now you have said this, it sounds more of a mechanical issue rather than valving? maybe time for a strip down and re-build

 

[lwsmithjr]

I've wondered about the binding issue as well. I tried a search but came up empty. My procedure has been to install the axle bolt and nut, make sure the pinch bolts are NOT binding, roll the bike forward and grab the front brake. Logically, I thought this would cause the wheel and all front end components to move into an aligned posistion. If this is wrong, please advise. (I did make sure there are no gaps in between the wheel and spacers)

I decided to tear it down New Years Day and recheck the oil level. I fiound that the level was well below 135mm in both legs. The only thing I can figure is That on the last seal replacement, I failed to bleed all of the air out. I've dumped all the old oil out, replaced and pumped until I was sure all air was out. I've set the level at 135mm. Now we are waiting on it to quit raining so he can try it -- If you guys have a recommendation on the alignment procedure, or can point me to a thread, I would really appreciate it.

 

[marcusgunby]

I think www.mx-tech.com has a guide in the download section.Its not unusual for the levels to be a bit different than when set-however you cannot compare properly as when you set the airgap after the seal replacement-you overfill the forks and suck excess oil out-you have a certain amount of oil between the inner and outer tubes-once you ride the bike this oil is now dumped into the main inner tube-normally giving you a higher level than when you replaced the seals.

 

[MXP1MP]

Well I'm not real familar with '01 YZ's but everyone claims its better than the '02's and the '03's are more like the '01's settings. I ended up getting my forks revalved in the end. My '02 compared to my '03 suffered more from midstroke harshness and yes the '03 has it too just not as bad. I finally got fed up with it I got tired of it feeling stiff then in like the last few inches of travel like the last 3 inches it felt like it just suddenly broke free and just about always bottomed out hard with a clank. It took me months to figure it out, I'm not sure exactly how the shim stack was modified. I justed asked for more plushness threw the entire stroke and better bottoming restance. When I got the forks back the oil level was set at 110mm's Compression 8 rebound 12 stock .41 springs. I also had the shock done with the same thing in mind. It made all the biggest difference the forks were alot more plush and even had better bottoming resistance and the midstroke harshness was gone. I'm going to eventually have this done to my '03 250F. My bud with an '01 250F claims that installing gold valves made a huge difference also. Isn't the midstroke harshness pretty much the norm for yamaha's?

 

[marcusgunby]

MXPIMP you do hear of midstroke harshness alot with YZs but i dont see anything that means it should be that way-the YZ has a larger catridge than the CR or KX and should be very tunable.Maybe its the Yamaha test riders fault

 

[russ17]

Marcus thanks for that bit of info on the oil level. I was just servicing a set of forks and I always check the oil level before sevicing I thought I was going crazy I knew I set them at 100mm before, there must be a good bit in the outer tubes because what i measured was around 85mm. Do you take this in concideration when you set your oil level. I have herd that some shops just put in OZ that probably why.

 

[marcusgunby]

As long as you always set them the same way, and you know that which system people are using when they quote a figure its no problem-i dont measure it after riding as i know they will be different-and not by the same amount.I read about people saying about setting the clickers eactly the same and altering the airgap by 3mm and i think??????you only feel the combined damping of the 2 forks-if one is slighly different to the other leg you wont feel it-the older KTMs have all adjustements on one leg(ie comp adjuster on one side and rebound on the other)and they dont feel like its lobsided.

Also on the showas you only use a volume measurement as its hard to measure airgaps on these.

 

[lwsmithjr]

We just got back from the track and I'm happy to report that it seems most of the problem went away. I set comp @ 14 and reb @ 10, level @ 135mm. Correct me if I'm wrong but if the oil level was drastically low, (and it was -- the rod I was using to measure was 150+ mm long and it did not touch the oil) the forks would ride down in the stroke, thus causing severe harshness and headshake. I did not measure the air gap after riding today -- and I don't think I'm going to.

Marcus, I downloaded the fork install instructions from Wilkey's site. Thanks for the pointer. It seems for the time being, things are working as they should.

Again, I'm dependent on his feedback. He says that it's tremendously better now. I may be back when we get a beat up track again -- kind of muddy today. Thanks for all of the input. You guys helped a lot!!

 

[marcusgunby]

The airgap sets how strong the airspring will be-the airspring is very important past half travel.

 

[lwsmithjr]

Okay, so I AM wrong (you don't have to be so polite Marcus -- I'm secure in my ignorance!!).

Well now I'm really confused. Maybe I did have them in a bind. Or maybe they aren't working any better now than before and he is just more used to it. Since it's undersprung for me (by 50lbs.) I'll just have to wait and see. If he continues to have problems, I guess I'll tear them down again and have a look at the valves....

 

[marcusgunby]

I always say leave well alone unless hes unhappy-if he says they ar eok then they are ok-i found out once when working with a rider that if you change stuff they can loose confidance-sometimes a bike thats slighly off is better than one thats different every week.

 

[lwsmithjr]

Good advice -- I'll let you know. And again, thanks for the help!