Service

SERVICE

JOE MINTON

Down sides of up sidedowns

I've just finished reading your “Built for Speed" article (OF. November, 1 990) and I got excited because 1 have a '90 FZR 1000. I plan to make some modifications, but I'm stumped on a few things.

I've heard such rave reviews of upside-down forks that I can't help but wonder which one is the best. What is the correct set-up, and after I dialin the fork, should I get a different rear shock?

I hope that you can help me in my hazy cloud of confusion; I don't know who else to ask.

Lloyd Hull

Stratford. Connecticut

In that same “Built for Speed" article, we highly praised the upside-down Kayaha fork mounted on the Yoshinutra GSX-Rl 100, and in 1991, all front-line sport bikes of 7 Mice and above, including the FZR 1000, will come with sonte manner of upsidedown fork. However, any change as fundamental as replacing the front fork of a motorcycle must be considered very carefully. Spring rales, damping characteristics and trail are all critical, not only to the handling of a motorcycle, but to its stability, too.

Even if you are capable of tuning a new front fork, the task is daunting. I recommend, rather, that you consider tuning the springs and damping of your stock fork to suit what you intend to do with it. You can accomplish much with the tuning options available.

Upside-down forks can be more stiff (resistant to flexing) and can have lower unsprung weight than conventional forks. Both differences are desirable. However, for the average rider; those differences are, for now at least, small. The cost of conversion and difficulty of making a new aftermarket upside-down fork work correctly for your bike and your performance needs make the whole business, in my view at least, much more trouble than it is likely to be worth.

Time to trade up

PI ease help me with a problem. We've got a I 980 Yamaha XT250 which I, as a 63-year-old with a little

arthritis in the knees, simply cannot kickstart. My Yamaha dealer fixed the disconnected auto-decompression device, but it made absolutely no difference. In fact, it seems even more difficult to start with the device connected. The only way I can start it is to push it up a hill, roll down and pop the clutch. This usually works.

I like the bike very much but am severely restricted with this problem. And no, I cannot afford a later bike with an electric starter.

Gene Mandel

Laguna Hills, California

The practical solution to your problem is, unfortunately, not very encouraging. An auto-decompression device works by holding the exhaust valves open for part of the compression stroke. This reduces the amount of fuel I air mixture that will get compressed and the effort it takes to do so. It also reduces the pressure in the combustion chamber at the time of ignition and the likelihood that the mixture will fire. The easier it is to kick over, the less likely it will be to start.

I must recommend that you consider another bike—either one with more and smaller cylinders or one with an electric starter. You should be able to find someone who would love to have your XT. It is a fine machine.

Your area has a regional weekly paper called The Recycler, where folks list (free of charge) hundreds of items for sale, including motorcycles. You

should be able to sell your Yamaha through this service and find a good, inexpensive machine like a I9S0 Yamaha XS400 with an electric starter at a reasonable price.

Hot ceramic coats

What do you know about ceramic plasma spray as used on engine parts (piston crown, valves, exhaust ports, etc.). Does it deliver on the claimed benefits of longer part life, more horsepower and better mileage?

Ted Lorenz Greeley, Colorado

Ceramic coalings do have an insulating effect because of their muchlower heat conductivity as compared to non-coated metals. particularly aluminum. Many of us have melted one end of a glass tube or rod over a Bunsen burner while holding the other end. Try that with aluminum!

However, insulators such as glass or the ceramic coatings in question are not perfect. They do allow heat to flow. You might be able to hold the end of a glass rod while melting the other end, but only if the rod is long enough. If it's short, you'll burn your fingers. The distance between the hot and cold ends matters.

Ceramic coalings are usually loo thin to afford more than a very small temperature drop from one side of the coating to the other. That temperature drop might make all the difference to a hot-running racing two-stroke engine's pistons. It won't mean a thing to your street envine. 0