Intro/ Forks

[123mclaren]

Evening Gentlemen

I've just acquired an 84' FJ600 from my dad. bikes got 19500km on the clock and purrs lick a kitten. Not hard starting but takes some time to get off the choke. My only concern with the bike is that the front suspension seems to lift up quite abit under acceleration and dive under braking. I\ve gone ahead and put in new 10w fork oil 9.5oz. Wasn't able to find any info about measuring spring length, springs seemed firm, there were no spacers. Went for a quick boot around the lot and noticed smoothing dampening, but still get quite abit of lift and dive. I will try to put 5mm-10mm of preload on the springs tommrow.

My question to you guys is: is this common on these bikes, can this be resolved with progressive springs, is it possible my rear shock is weak and the weight is transferring to the back. REar shock seems firm.

A little out me. I own 2 1976 Honda CB400/4, my favorite bike since I was 4. also building a yamaha RD350. The Fj is my biggest bike to date and im looking forward to a few 300+ mile trips with it. Hope you guys can help a newb out.

Cheers
Alastair

[simi_ed]

Based on my & others experience, I'd avoid progressive springs, & go with straight rate springs.  Further, I'd look to Race-Tech for suggested upgrades to your forks.  Good luck & let us know what you find.

[Arnie]

Hi 123,

There are very few FJ600s on this list, but the principals of telescopic forks are pretty standard.
You should put in the "proper" spring rate for the combined weight of your bike and self.
Next you should set the amount of preload so that you have static sag in the range you want and need.
Finally, you should determine what viscosity oil to use. 
A higher number viscosity oil will provide more damping, and a lower viscosity oil will give you less.

Then you run into the choice of modifying your fork internals with RaceTech valves or similar.
All these various changes interact and there is no one "right" setting.
There ARE guides to help you set your suspension online and in the files section here.
Search "Suspension Setting" and try to understand how this all works.

Note: If I've been talking too basic for you, I appologize, I don't know your knowledge level.

Cheers,
Arnie

[movenon]

I agree with Ed. Go to Race Tech's site and see what they recommend for straight rate springs.  I think you will be surprised.
George

[FJmonkey]

Check with Randy at RPMracingca.com. He might have some good advice as well.

[123mclaren]

Wow.. Thanks for all the responses guy. Quite the community.

Ive used race-tech springs and emulators in my CB400f racer. Great units but a little pricey as our Canadian dollar has dropped. Regarding the progressive springs, my bike has progressive wound springs in it currently, not sure of the weight or manufacturer. Would this bike have come with progressive springs stock? I replaced the oil and I will try some spacers soon. I'm not looking to make this think a caddy just want less dive and less lift. Was mainly wondering if anyone has experience with a stock FJ600.

Good call on the static sag measurement maybe can play around with that and the spacers this weekend. I guess I can also try a thicker oil maybe 15 wt.

Thanks again, Ill post some updates soon.

Cheers

[Troyskie]

I've recently gone through the same with my 1100.
Progressive was the way to go in the 80's, but stiffer straight springs plus emulators stiffens up the front and improves ride quality dramatically.
BTW-This replaced progressives that came with it. Prior to this I was a progressive believer (now I'm not).
Not sure what to suggest for a 600 though  .

[fj1289]

If you want to experiment - it is possible to cut the progressive springs to remove some of the closer wound coils (the weaker part of the spring) and then replace it with a spacer of the same (or slightly longer) length.  This will stiffen the spring by removing some of the lower-rated coils AND by decreasing the number of "active" coils.  You do need to watch out for coil bind if you take too much off...

[Matt Rain]

I had quite a bit of dive on my FJ600 when I first got her. Simply changing the oil (to 10wt Motul Fork Oil Expert) made a dramatic difference. It actually felt a little harsh until I reduced the preload at the rear (from 4 to 3).

I believe my springs are OEM, and from memory, the spacers are a good 1.5" tall if not more. I would experiment with spacers before investing in new springs, that may be all you need.

[Arnie]

Regarding the progressive springs, my bike has progressive wound springs in it currently, not sure of the weight or manufacturer. Would this bike have come with progressive springs stock?

Don't know for sure on the 600, but the FJ11/1200s came with progressive springs (rate varied over the years).  Straight rate springs work better.

I replaced the oil and I will try some spacers soon. I'm not looking to make this think a caddy just want less dive and less lift.

Once you set the sag and change oil, you can experiment with adding extra oil.  This will give you a smaller trapped air pocket above the oil which will make the last part of the travel at a higher effective spring rate.  This should cut down on the amount of dive.  Change in incriments of about 10mm. However this is a "fine-tuning" item, you really need to get the proper spring in the fork first.  Oh, last point would be that you should stick with a single brand of fork oil as the 15W oil of one maker may be different than a 15W oil of some other oil brand.

Arnie

[Mark Olson]

Great info already posted by everyone ..... just a quick tip for adjusting fork oil level is to measure with the springs out and forks compressed . Take the measurement from top of fork to oil level inside . That way you can use a turkey baster to remove oil or add when fine tuning your oil level , use 5mm adjustments. keep a record where you wont lose it.