Motorcycle Suspension Help

I've got a question for you motorcycle gurus out there. I want to upgrade the suspension on my 2002 Katana 750 and am having trouble with some of the specifics. I'm a member of a Katana forum also but everyone over there assumes everyone else races their bike so I can't get any decent feedback on an entry level upgrade (in TW suspension speak, everyone there thinks everyone needs a full LT setup when in fact plain old 5100's will do).

I've found that the stock suspension rate is .65kg/mm and to have the bike setup for my weight, it should be closer to .90kg/mm. I've located a set of springs and want to open up the fork, swap the springs and close them back up. The other site is telling me I need to replace all my seals and get cartridge emulators as well, which effectively doubles the cost of this upgrade. I don't think I need new seals since the bike has under 9,000 miles on it and aren't showing any signs of leaking or deteriorating. I don't think I need the emulators because truth be told, I'm a mildly aggressive street rider at best and will most likely never see a race track. I feel for my needs the stock dampening adjustment would be sufficient but I can't get anyone with any kind of motorcycle know how to give me sound reasoning why I should or shouldn't go with the cartridge emulators.

So, who's the resident motorcycle suspension expert?

 

Not me. I replaced my SV shock with GSXR shock. Free bump though.

 

I've heard that the R6 shock is a decent upgrade for the Katana 600s but the 750's rear shock isn't half bad from the factory. It's got a decent amount of adjustment built in. Just trying to make it so the front end doesn't disappear every time I touch the brakes!

 

Admittedly I know nothing of Katana's but if you don't need seals or race tech emulators, don't bother.

Suzuki's fork springs are normally a "progressive-rate" spring, meaning weak as hell extended and stiffer as they compress (in theory). As far as changing out your springs, you'd be a lot better off if you removed the forks from the motorcycle. It can be done, one at a time if you choose not to though. Problem is setting the oil height, normally the forks need to be collapsed for an accurate measurement.

What kind of help do you need exactly? The emulators? Normally unless you are racing or a track-day addict you won't need them. What kind of adjustments do you have now? Rebound only? If that's the case emulators will allow you to dial in compression dampening but only while the forks are dis-assembled....which IMHO, is normally more of a pain in the ass than what it's worth. You can get relatively close playing with the fork oil height to add some "air spring"/compression. Warning though, go to high and you WILL blow the seal out.

 

You need springs and a little higher oil height most likely. A few mm's of extra oil will give a hair more compression/air-spring. Either way, the fork springs support the weight of the motorcycle with you on it... If you are an aggressive braker, then you need some sort of adjustability for compression, or take it to the local suspension/tuner shop in your area and talk with him.

 

I bought a pair of non-progressive 1.0 kg springs from Racetech and installed them without cartridges. No problem. The new springs were 1" longer than the OEM so I had to cut down the stock spacer. I did a step-by-step tutorial on the FZ1 forum if you're interested in viewing it. The FZ1 has USD forks. Check http://www.fz1-forum.com/forum/susp...n-notebook-w-penske-usd-forks-diy-manual.html and the forks start at post #71. You need to be signed in to view the pictures.

FWIW, I did replace the seals and dust caps because they are cheap and how often do you get to take the forks apart?

 

I went back and looked at the pics from the handlebar conversion... You don't have USD forks so yours are even easier to do. Do you know the diameter of those? I have a 41 and a 43mm fork seal driver.

Mike, I don't know how far you are from Dover, NH but you're welcome to ride it up and we can swap the springs in the garage. You'll need help finding the static sag so you can figure out how much spacer material to cut. Racetech *should* include the spacer material with their new springs. Cost is about $110 for the springs and whatever you can find for deals on fork oil (no more than 7w but typlically 5w) and the cost of seals and dust caps. I think yours will need bushings too. USD forks don't require replacement of those.

 

Good info on setting the oil height slightly higher! I'm not an overly aggressive braker but man the front end dives when you touch the lever. My main question was will changing the springs and not doing the emulators be a worthwhile upgrade or is it the emulators that really make the big difference.

Fortunately, my forks are right side up so you can get to the emulators just by popping off the top cap and pulling the spring/emulator out if you need to. What I don't like about the emulators is you have to drill out the fork internals so there's no going back to stock. I figure I'll go with the springs for now and maybe the emulators down the road.

I'll take a look at your build, I really like the FZ-1. From what I hear, the new Racetech springs come with custom sized spacers so you don't have to hack up the stock ones.

I hear you about the seals but here's the catch... I'm going to try to do this without completely disassembling the fork. My forks are right side up so I'm thinking I can just pop the cap, pull the spring, replace with the new spring, set the oil height and off I go.

 

Thanks for the offer man! I'm about 2 hours from Dover so not bad. I finally bought a house last summer so I actually have a garage to tear the bike down in so if I go through with it I'll most likely tear down there and leave it on it's center stand (with weights over the rear of course).

I'm not sure of the fork size off hand, I'd have to look it up but yes, right side up forks will make for a pretty easy swap I think. There's actually a write up on the Katana forum where they show how to use a 2" piece of PVC as a seal driver

Based on this thread:
http://katriders.com/vb/showthread.php?t=90203
Here's the parts list I'd need (minus the emulators)
Race Tech emulators: FEGV S4101 (sold in pairs)
Race Tech Fork Springs: FRSP S353490 (sold in pairs)
Race Tech Inner Bushings: FMBI 41201 P (sold in pairs)
Race Tech Outer Bushings: FMBI 41152 P (sold in pairs)
OEM Oil Seals: 51153-08D00 (2 needed)
OEM Dust Seal: 51571-41D50 (2 needed)
OEM Brass Crush Washer: 51148-36011 (2 needed)
OEM Fork Cap O-ring: 51117-12C00 (2 needed)
1030mL of your choice fork oil (Suzuki spec is 513mL per fork) (Race Tech recommends 15W @ 4" down)

If I did a complete rebuild, I would need inner and outter bushings.

 

If you don't do track days, the emulators are probably overkill but if you've got the money, you won't regret the ride!

After the Penske 8983 and these new springs in the front, my bike is absolutely planted in the corners. I have the rear dialed in but still working on the front settings. I'm trying to find a happy medium between high and low speed compression. Rebound is already dialed.

Last, I think I may have to pull the spacers and cut more off. I cut them just a bit long and now I have too much pre-load and not enough adjustment to set static sag to 15mm.

 

Mike this off topic but I used to own a katana 600 I have a carb kit (not sure if it will work on the 750) but if you want it . It's yours . It's been sitting in one of my toolboxes for years now . I upgrade my exhaust but never installed it . Then sold the bike .
Just throwing it out there . I'll double check to tonight when I get home from work to see if it works on 750s
Good luck on the suspension upgrade .

 

That's encouraging to hear! Good luck with getting everything dialed in. From experience I know it's a lot of trial and error, no set formula for every rider. I'll give some thought to the emulators. I'll probably do the springs and oils now, and the emulators when I do a full rebuild over this or next winter. The emulators require you to braze the stock components which I don't have the tools to pull off.

Thanks John! I'm not sure if they'll fit or not but I just had new carbs put in a couple years ago and I won't mess with the carb bank myself. There are a lot of Katana riders in the area so if you want me to list them on that forum so you can get some cash out of them, I'd be happy to help you out with that.

I actually got really lucky when I bought the bike. I bought it used from a dealership and it had an exhaust and the intake/fuel delivery was stock so it ran like crap. The dealership installed a stage 1 kit under warranty to make it run better. It really woke up the exhaust, killed my MPGs and the bike runs smooooth now

 

Ya that would be great . Ill find some info on them and pm you .

 

I got some tips from a suspension pro that might help you too. He said to start working with 5 clicks at a time. This is an extreme change but how it works is if the bike feels to soft on compression, go hard 5 clicks. If if is better, go 5 more. Worse, start backing off 3 clicks, better? worse? you get the idea. The principal of this is that one or two clicks are hard to tell the difference between where 5 is very noticeable. This is what I am working with on the compression leg. He also said to nail rebound first then compression but never try and adjust for both at the same time. So far, I like his wisdom and it's working great! I'm down to a three click movement on COMP now.

Good luck! If you need help, I can try and be there. Where in MA are you again?

 

That's great info and a sound way to setup a suspension setup to a non-racer! My issue is, the forks do not have a compression adjustment, only rebound and I believe I only have 4 or 5 clicks of adjustability The rear has a lot more to mess with so I'll try that method with the rear and see how it goes. The front is too dumbed down since the Katana is sort of a fake sport bike or a sport tourer.

I'm living down in Millis, about an hour W/SW of Boston.

 

Have you checked into what other forks might work with the bike? Maybe a used set of forks from a newer bike that has full adjustments? A lot of the FZ1 crowd moves up to the R1 forks. 2002-2003 are a bolt-on. Anything newer and I'd need to get the wheel, axle, rotors and calipers. Ebay front clips can be snagged for $300 - $450 and the difference in both ride and stopping are incredible. I don't know what fits the Katana 750 though.... Maybe a GSXR 600 front? Just a thought before you buy.

 

I believe one of the GSXR forks can be used but it requires the whole front end (forks, axle, wheel assembly and triple tree). Because the Katana's forks are right side up, it's tough to find a high performance fork that just slides in. The most cost effective solution is springs, oils and emulators but a full front end swap can be done if one were so inclined

I'm avoiding doing that because I just picked up the handlebar kit for this triple tree and the riding position is awesome! It's like having the best of both worlds, a sport motor and upright seating.

 

Just got pricing on the whole setup:
Oil Seals $22.00
Dust Seals $21.00
Fluid $13.00 per liter (1 liter required)
Copper washers $2.00 EA (2 required)
Emulators $145.00
Springs $100.00

Not terrible, might have to wait til winter though. This would take me a few minutes to install and I won't want to be down for the riding season.

One more thing to add... If I go with emulators, I'll end up losing the rebound adjustment permanently.

 

You could do all but the emulators and see how well it responds. It shouldn't take more than an afternoon. Cheap enough!!

 

That's what I'm thinking. There's a Racetech dealer on that forum who gave me those prices. They're a lot cheaper than buying through Racetech