Air compressed front forks

I bought a 1982 KZ650 CSR a few months ago and have really enjoyed working on it. The engine runs well, but of course, little things keep needing to be replaced. I'm also finding that some of the parts are not original. My master cylinder, for example, came from an earlier model Kawasaki. (That's what I get for buying used without a bike history) Anyhow, the newest challenge are the forks, which have gone soft on me. I checked my manual, bought some fork oil, watched a video on YouTube about how to do it, pulled out my manual, and discovered that my forks aren't original either. Their air compressed. So, I'm not sure what to do at this point. I don't know what bike they were "parted" from, so I don't know the specs of the forks, nor how to fix them. Ideas?

Here's photo of the top end. Under the cap is an air valve.

Tariq4:

I have the same motorcycle, and the photo of your forks look identical to mine. Mine also have air fittings, exactly like the photo. To me, they look like the right ones for the bike.

If you remove the phillips screw near the bottom of the forks, and allow all the oil to drain, then refill with about 260 cc. of 10 or 15 weight fork oil. If you disassemble the fork internal parts, then add back 280 cc. +/- 4 cc. There is a retainer that goes on top of the spring, and then a spacer that measures roughly 3" long that goes on top of the retainer.

I had to replace my fork seals, in order to keep from loosing fluid and to keep it off the brake disc, etc.

I usually run from 10 to 18 PSI of air pressure in my forks. With no air, the ride height is too low, and they will occasionally bottom out. Send me a PM if I can help in any other way. Good luck.

Bleed off any air in the forks before unscrewing the drain screws, otherwise you might get a spray of oil and air!

MFolks wrote:

Bleed off any air in the forks before unscrewing the drain screws, otherwise you might get a spray of oil and air!

Thats an affirmative! :laugh:

Use proper amount of oil, then add/remove air for your riding pleasure.

Just remember not to use a compressor to inflate, as more than 30psi can damage the seals. Bike pump is good, and make sure to have a very accurate guage as same amount in both shocks is critical to handling.

GL.

Tariq4 wrote:

... (That's what I get for buying used without a bike history) ...

No one should expect that when buying a vintage bike. And don't believe anything the previous owner said either.

As for the forks, they're most likely stock - 99.99% probability.
Maybe some of the other stuff on the bike that you believe is not original is stock as well.

I rebuilt the air forks on my CSR a couple of years ago & added ~14psi at the time. I rarely check the pressure - it's too much of a hassle trying to get them aired up the same. Bill above installed a neato homemade air equalizer.

If you take the forks apart, you can measure the springs to see if they're within spec.
The stock springs are kinda flimsy. An improvement to simplify things is to get new progressive springs & eschew the air. The recommended fluid is 10W fork oil, but heavier could be used (I put in 15W fork oil; some folks use ATF).

Thanks so much! I guess the top of the forks threw me off as it doesn't look like you can just drop a ratchet over top to remove the cap with the air valve there. Well, that, and the air compressed label near the bottom.

Some of the other parts have caused me heartache though...like when I ordered a new diaphragm for the master cylinder to discover that the master cylinder on my bike belongs on a GPZ with a different sized diaphragm. I also just recently discovered that one of the wires connecting to a spark plug is different than the other three.

New to motorcycling, so I have a lot to learn, but I'm trying to do as much as I can myself instead of going to a garage. I'm loving it!

Thanks again!