Defeating fork air system?

I have another KZ (KZ650) that I rarely post about, as it is in good shape. But I have had problems with the air/oil forks. Even though the seals are good and don't leak, they are usually out of air on one or both sides when I check it. Others I have talked to say that the air/oil system that apparently many manufacturers went to in the early 80's is a poor design, and I have heard of some who defeated the system by adding a spacer above the spring and not using air at all.

Has anyone here done this, did it work, and what length of spacer did you use?

I got tired of messing with the air on my 81 KZ1000 CSR, Wouldn't hold two days. Forks would bottom out on a hard bump. I put a pvc pipe spacer, I believe it was 2 inches long, on top of my springs. I was gonna buy some Progressive replacement springs, but the spacer works so well, I don't need them.

I can pretty easily start my fork caps into the threads with the stock setup and the forks fully extended, and they get tight about half way down. I'm wondering if I'd have trouble getting the caps in with a 2" extension?

I don't really know if my present springs are stock (there are no markings), but the coils get wider at one end. Maybe that's stock and not prograssive.

Yea, I loose the air in about the same time, although the seals (just new) don't leak. New or not, I suspect that is where the air is getting out. If I can get the caps back in, I might try the spacer idea.

"Progressive" is a brand. www.progressivesuspension.com/
I guess all of the stock springs are progressive in type of spring
In some of the "Progressive" applications, they come with instructions on how to calculate spacer length which is on their website.
Mine is probably longer than necessary, but I figured if a little would do a little bit of good then a lot would do a whole lot of good. Too much would be just right.
I remember having a little bit of a struggle getting the caps back on

What size pvc pipe was used as a spacer I would like to do this befor I head to sturgis.

I bought 2 1/2 inch cuplings they look like they will fit ?.
and they are thicker than a single piece of pvc.

Thanks in advance for the info :woohoo:

This topic was started a while ago. Since then I got a response on another forum (I think) that said to use old 750-4 valve springs (both the inner and outer) on each side above the stock washer.

Interesting! Anyone ever try this?

I used some 1" that I had laying around.

Thanks for the info !!!

I hope this helps my forks are way to soft !!!


If I had the left over springs I would try that method

One more Question .

So I pull the screw at the bottom drain the oil then pull the fork cap . // Right
Then cram the piece of pvc in and put the cap back on .

OO and add oil. :S

No need to drain unless changing oil. Be sure to relieve the air pressure.

Keep in mind that adding a spacer above your spring, which increases the preload, is not exactly the same thing as adding air. The spacer only increases the preload, thereby reducing sag when bike is loaded. Adding air increases the preload and effectively increases the spring rate throughout the entire fork travel. It also has a progessive nature , as the effective rate will increase as the air chamber volume decreases (fork compression.

FWIW, the stock springs in the air fork equipped bikes are typically 50%-60% of the spring rate of what a proper non air fork bike would require. My 550 comes with .490 kg/mm springs, but the reccommended rate is .950 kg/mm

have you checked the shrader valves/valve cores?