YZ125X did not run fork springs?

[John Orchard]

Correct me if I'm wrong, but the YZ125X did not run coil springs in the forks?  Yeh I know it had the chambers on the top of the forks, with a floating piston with an airvalves above & below it.

Other bikes (RM-B & KX-A5) with soft main springs that used air, to increase the major springing tension, ran long top-out springs; I guess air pressure was not supple enough over small bumps?

Can anyone attest to how the X forks felt/performed? Any feedback on what pressures they ran?

[Paulos]

They didn't run springs. Feedback I've read from back in the day said they were good when set up properly.

I've converted mine and just run springs with conventional fork caps.

[80-85 husky]

air has a progressive problem when run straight in the forks, 75% soft then too hard as the air is finally compressed in the remaining space. Yamaha worked to beat this with the two chambered air valve, 1 to control low pressure suppleness and 1 to manage the hard compressions. getting them right wasn't easy due to small pressure differences having big effects but they were effective and as good as any of the others and you didn't need different springs etc.

[LWC82PE]

They didn't run springs. Feedback I've read from back in the day said they were good when set up properly.

That's pretty much what i have read too.

I guess you could fit some of the soft springs from the 77 RM125 or any of the 78 RM's or maybe get lucky and find some universal Fox #39-2000 10lbs springs which they sold specifically to convert 35-36mm forks to air spring set up. I found a NOS set plus a used set in some 76 RM forks.

[Iain Cameron]

John all the 76 models used just air once you set them up they are great . Ive got the 125x 250c and 400c all great bikes . Iain

[Momus]

Fox air rear springs are twin chambered, differential pressure principle as well.

[John Orchard]

Thanks Guy's  :-)  The reason I ask is, my KX250/400A5 now has the stock 38mm forks back in (now fully legal Evo), I thought I'd try them with the .24 kg springs removed, still running the long, soft top-out spring, and run only air.

So far they feel great, I ended-up settling on 50 psi, they don't feel any worse than the stock set-up and now I've lost a couple of kilo's in weight.

I was worried about gas leaking-out but with one ride and the bike sitting around for a week, I've only lost 2 psi.  I was thinking about bridging the two caps so that I only had to set/check the pressure once but should I have a leak/blow-out, then I am stuck with a totally bottomed-out front-end.

[shelpi]

interesting, yep always checking the pressure in the RM125B, to be honest my set up for my weight with oil amount and weight I tend to run low psi (back in the day) ahh the good old days with no valves in caps had to undo caps to let the air out when the forks got hard

[80-85 husky]

check the Monroe air car shocks, they have a central filling valve setup, I had one on my xl years ago when I tried it.

[Iain Cameron]

The problem if you link your forks is if you only use air then if one goes both drop to the bottom of the stroke . unhappy state on landing from a jump . Keep them as separate units . Iain

[LWC82PE]

check the Monroe air car shocks, they have a central filling valve setup, I had one on my xl years ago when I tried it.

Makes sense. S&W had an air shock line for road bikes which were made by Monroe and explains why the S&W 'air balance' fork and shock kits sold for motorcycles in 70's/80's which i have, use the same tiny black nylon line and fittings as what was supplied to me when i went asking for some more of it at a local car suspension place. They had exactly the same stuff.  I think he had the T-fittings too but i did not need any so did not ask for them. Goki also had their 'equal fill' system as well which was similar but used larger nylon line, first with brass T -fitting and a schrader, then later a lighter blue anno alloy t-fitting.

[FourstrokeForever]

RCH Suzuki also trialed the same "central filling system" with Ken Rockzen last season and it failed. it was the only race that he didn't finish on the podium all season.

Keep it simple would be my advice

[Big Scotty]

Some time back when I was a teenager apprentice we would get fittings out of the store at work,screwed straight into fork caps,a t piece that we silver soldered a valve stem out of an old car tube into it and joined them with blue nylon hose,looked pretty trick,never had one blow out and every one we rode with had a set,never any trouble
Cheers scotty

[John Orchard]

Ok, they say 'you never stop learning', so, l took the springs out of my stock KX250A5 forks, put 50psi of air in, hmm feels good, left them for a couple of weeks, didn't lose any air, beauty l think.

The workshop manual says "Do not run air pressure any higher than 36psi or seal damage will result", me thinks that the 'damage' would be that the seals would leak air or oil, well no, the high pressure caused the seal lips to flatten-out causing incredibly high seal drag!

So, back to using springs :-)

[Rossvickicampbell]

50 is very high though isn't it John?