82' Seca 650 suspension rebuild

Just bought an 82 650 Seca with unknown mileage. I'd estimate 15K from the brake rotors if I had to judge anything. The bike is getting a general refreshening, but I'd like to see what suspension recipe experienced Seca riders have come up with. I have always read about how soft the front forks are. I weigh 185 pounds. So is there a fork spring length and stiffness that works well for general two lane street riding? Would I have to change valving or just fluid weight to get the spring dialed in? The rear shocks look to be in very good condition. Can they be tweaked and or rebuilt by a suspension expert, or should I just get aftermarket? Was also thinking of a Fork brace, tapered steering bearings and stock sized tires , either Bstone BT45 or Metzler Roadtek 01. Opinions greatly appreciated.

 

XJ forks are damper rod forks, IMO the best upgrade for them is from "Race Tech" They sell a product called "emulators" it's a valving system that simulates the action found in modern cartridge style forks.
Fairly easy to install or you can send your forks to them, and great tech support. I've used them in four different bikes so far and they work very well.
They also sell the proper springs for your bike and rider weight along with seals, fork oils, everything you'd need. I would visit their web site and look up the XJ under the Vintage categorie. Most older bikes are unsprung to begin with. Race Tech
are a wealth of knowledge for suspensions of all types and will help with any information you may need. I'm not a salesperson or connected with Race Tech in any way.
Cheers, 50gary

 

Thanks a lot Gary, I have heard good things about emulators. Do you have this setup on your bike?

 

Not on my 750 Maxim (2000 R1 front end) but on my Suzuki T-500 that I've swapped to 94 Katana 41mm forks, yes, FZR600, Dt 250 converted to RD400 forks with emulators, My Brother also has a T-500 with GT 750 forks with emulators.
Race Tech springs as well on all these bikes. "Mike's XS" sells some bargain priced emulators, I have not tried them.
Cheers, 50gary

 

My experience so far. Became the owner of 3 Seca's, last Summer, made one road worthy. In process of servicing bike to be ready to ride, found that PO had installed a set of Progressive fork springs which are stiffer than stock, did not think too much about it, took it a a plus, 10 weight fork oil. After several short shake down rides, I finally got a ride in that was more than a short hop, 200 miles worth. I live in New York state, finger lakes region, roads are OK, could be better, could also be worse. I too weigh about 180/185 pounds, with the rear shocks set one click up from softest setting, I thought the bike rode like a buck board over expansion joints in the road. I plan on changing fork oil to 5 weight to see if there is any improvement in ride quality, may look to see what the springs are in the other two bikes, maybe one of them has a set of good stock springs I can try.

 

Spoke to a fellow at race tech who handles the vintage bike questions. Turns out he had a Seca 650. Suggested that the gold valves and their springs would offer great performance. When I had my Seca brand new and weighed 150 pounds I thought it was too soft back then. I liked how he explained the gold valves. You adjust compression damping with a screw setting and rebound damping with oil weight when running these emulators. Of course many ways to get things wrong too I suppose, as I know very little about suspension tuning on bikes and what works best. I'm still researching bits and pieces for this bike, so I'll have to get it running and stopping well first. This might take several months

 

The oil level may be too high as well, oil doesn't compress, air does, more air = softer. The proper/reliable way to set fork oil level is to have forks vertical, (out of bike) springs out and forks compressed. Then measure from the top edge of fork tube down to the surface of the added oil. Race tech will tell you the proper level to fill. It's also important to get both to the exact same fill level. The springs could have too much of a top load spacer. Using vernier calipers measure the diameter of the spring wire and compare it to your other stock springs.
Cheers, 50gary

 

If you get the fork working as well as it can with updated parts, will a stock back end be a total letdown? From appearances, my rear shocks look to be in excellent condition. If they are not up to the task of spirited street riding, what shock options are well proven on the 650? Perhaps shocks from another model ? Seca 900?

 

Yes, original rear shock are dreadful. Ikon (if you can find a set) adjustables, or Hagon are ones I've tried an liked.
You can spend hundreds on remote reservoir gas pressurised ones, I'm not convinced the xJ needs them.
When I rebuilt my Kawasaki front tubes (having never been inside one before), I was amazed how basic they were, so these inserts are on my list for my seca and my maxim, the vmax will have to wait for a leading link.

 

As long as they still have dampening in them I would give them a try first.
Brand name shocks are expensive, I would wait until everything else is sorted before spending the money.
You said they were set on the softer end so try adding some preload.
The 900 shocks are about 1/2" shorter so are not a direct swap.
I like what you're doing to improve the forks, but again you could start just with stiffer springs and see how you like the ride.
The cartridge emulators can be done later but stiffening it up makes a lot of difference.
Moving it off the centre stand with the stock springs already eats up 1/2 the suspension travel.
Everything on your list is good but make sure you add new SS brake lines.

 

Yes, first I must get it running. It's been sitting for years and years in a showroom window. I'm going to rebuild the hydraulics, new rear brake shoes, stainless lines. New tires. Fingers crossed the carbs come back to life decently. So far as I take it apart, everything is looking very nice. Would probably have made sense to buy the best one I could find that is sorted out. Most likely cheaper in the long run.