Service

SERVICE

Paul Dean

Hard-chargin' ZX

I have a 1990 Kawasaki ZX-11 that I purchased brand-new. I am experiencing a problem with the battery boiling dry on extended rides, especially in warmer weather. This has occurred with both the original battery and a replacement. I’ve contacted my dealer about this problem, but have had no luck coming up with any kind of solution. Do you know if this is a specific problem with the ZX-11, and if so, do you also know of a fix?

RJ. Hartman Omaha, Nebraska

I’m not aware of any such problem with ZX-1 Is; but based on the limited diagnostic information you ve provided, I’m fairly certain that your bike’s voltage regulator is malfunctioning. The regulator is permitting more than the maximum allowable current to reach the battery, thereby creating excessive heat that cooks away the battery ’s electrolyte and warps its lead plates. This is exactly the same kind of damage the battery would suffer it it were charged by a high-rate, garage-type charger intended for automotive use instead of a low-rate charger designed specifically for small, motorcycle-style batteries.

To verify that the regulator indeed is at fault, you first need to get your hands on a shop manual for a ZX-11 (or a ZX-10, which has the same charging system) and subject the regulator to the series of simple diagnos> tic tests clearly outlined and illustrated in the electrical section.

On these Kawasaki models, the regulator is a small, solid-state unit contained within the alternator assembly, which is located behind the cylinders at the base of the cylinder block. To access the regulator, you have to remove the outer cover on the left end of the alternator, as well as the coupling drive disc that sits beneath it. This exposes the regulator, which is removed by undoing the small Phillips screws that secure it to the alternator. Once the regulator has been extracted from the alternator, you can readily perform the necessary diagnostic tests.

Rakish inquiry

I keep reading references to “rake” and “trail” in Cycle World and other motorcycle magazines, but I haven’t been able to find anyone around here who knows exactly what those terms mean. Lots of people I’ve asked think they know, but the explanations vary so much from one person to another that I’ve come to the conclusion that no one really knows. How about a layman’s explanation? If you haven’t room in your limited space, could you recommend a book? Andrew Potter Glens Falls, New York

Rake is comparatively easy to comprehend: It refers to the angle of the front fork tubes relative to a vertical plane. When a bike is said to have, say, a 27-degree rake, this means its fork tubes are angled 27 degrees from vertical.

Actually, the term “rake” often is misunderstood and therefore misused. One of the crucial elements of a motorcycle’s front-end geometry is its steering-head angle, which is—just as the term implies—the angle at which the steering head is attached to the frame relative to a vertical plane.

It just so happens that practically all modern motorcycles have their front forks mounted at the exact same angle as their steering heads; so, in the case of those particular bikes, “rake ” and “steering head angle ” are, for all intents and purposes, interchangeable. But every once in a while there comes along a bike that has its fork legs mounted at a slightly different angle than its steering head. Obviously, then, any time the rake differs from the steering-head angle, those two terms are not interchangeable.

Trail is harder to understand than rake, since it deals with imaginary reference points. But despite not being perceptible to the eye, trail has enormous impact on a bike s feel and handling.

To figure trail, imagine a line that passes through the exact center of the steering head and extends until it intersects the ground. Then imagine a vertical line that passes through the center of the axle and also intersects the ground. The distance between the points where those two lines intersect the ground is the trail.

I know of two books that offer rational explanations of motorcycle steering geometry: “Motorcycle Chassis Design Theory and Practice ” by Foale and Willoughby, and “Motorcycle Engineering” by PE. Irving. The former is newer and deals with matters that are more relevant to today’s machines, but Irving’s book is a classic work that all motorcyclists interested in technology should read. Both are available from Classic Motorbooks (800/826-6600).

Tariff bulbous

Last week I went to my friendly Harley-Yamaha-Kawasaki dealer to buy a light bulb for my Kawasaki KLR650 and was quoted a price of $57.49. After I recovered my teeth from the floor, the salesperson said he could sell me the same bulb from Honda for just $5.98! Does this hold true for other Kawasaki parts?

William F. Frazine Yucca Valley, California

Not at all. Either the parts person misread the retail price list or that list contained a whopping typographical error. Kawasaki’s suggested retail price for the bulb is $5.99, and the bike shops around our offices sell stock and aftermarket bulbs for between $5.99 and $10.95.

Foul play

My ’92 Suzuki GSX-R750 is giving me fits. It runs great when everything is right, but it fouls either or both of the two inner sparkplugs on the average of about once every 50 to 75 miles. The fouling usually happens while I’m starting the engine after it has sat overnight or over a weekend. The two outer plugs have never given me any trouble, but those two inner ones foul all the time. This is a serious problem for me, because I rely on the bike to get me to and from work, which is a round-trip of about 30 miles every day.

My dealer changed plug brands, and he even installed the next higher heat range to try to fix the problem, but they fouled, too. He says he has checked the compression and there is only 7 psi difference between all the cylinders, and that the cylinder with the highest compression is one of the ones that fouls plugs all the time. The engine doesn’t smoke, either. I’m stumped, and getting weary of fighting this problem. Any suggestions?

Geoff Deray Secaucus, New Jersey

One of your GSX-R’s two ignition coils is producing an exceptionally weak spark. The plugs foul on startup because the excessively rich fuelair mixture needed at that time creates a greater electrical resistance inside the combustion chamber. If one of the coils is weak, it cannot produce sufficient voltage to jump a spark across the plug gap through that added resistance.

As with most four-cylinder motorcycle engines, one coil on your Suzuki fires the two outer cylinders, and the other coil fires the two inner cylinders. Aside from the coils, everything that could cause recurring plug fouling would affect either one cylinder or all cylinders rather than just the two inner cylinders.

If you need further proof that the inner-cylinder coil is the source of the problem, simply swap the two coils. Do this by reconnecting all of the coil wiring, including the plug wires, so the coil that now fires the inner cylinders fires the outer ones, and vice versa. If the outer cylinders then begin fouling plugs (which I’m quite sure will happen), you’ll have ironclad evidence that the suspect coil is in fact the culprit.