Q I have a strange problem with the electrical system on my 1982 Suzuki GS1100G, which I have owned since new. At idle I get 13-plus volts, but when I rev it up, voltage drops to 12.34. I have a new rectifier/regulator. Is this normal? I expect it to be the other way around. The alternator gives voltage per specs: 90 with no load. I am an engineer working with power generators for a living and this little system is getting on my nerves.
Ari J. Feliciano, P.E.
A The good news is you're looking at an elementary electrical system, so tracking down the problem shouldn't be too hard. According to Trent Kirby at Electrosport Industries-purveyors of various fine motorcycle electrical components-90 AC volts from the stator is perfectly fine. You're probably looking at a bad voltage regulator/rectifier, a short in the wiring harness or a sick battery.
"There could be a faulty diode on the rectifier side of the regulator/rectifier," Kirby says, "but that would typically drop you to 9 or 10 volts because it would be charging on two phases instead of all three. And if the voltage regulator side of the regulator/rectifier were bad, the bike would be overcharging." The only things left are the wiring harness and the battery. There could be a short in the harness, with two or more wires coming together to drop voltage when you rev the engine. "I would connect the three wires from the stator to the yellow ones on the regulator/rectifier, then connect your ground wire and power wire directly to the positive and negative battery terminals. This factors out any shorts that might be coming from your stock wiring harness, narrowing the list of possible problems to the stator, rectifier and/or battery. The only way to really check the battery is to have a local dealer do a load test." Check the Technical Resources Library at www.electrosport.com for a solid explanation of exactly how your charging system does what it does.
Q After checking out some supermoto DVDs, a question came to mind that I thought was worth asking: Why are there significant differences between the offered lines of dual-sport and supermoto bikes? Both are supposedly intended for both street and dirt, yet it seems the supermoto bikes have tires that work better on pavement than a dual-sport's knobbies and the supermoto bikes seem to be almost all singles of relatively small displacement. Doesn't it seem that supermoto bikes are really the true "dual-sport" motorcycles? They actually are raced on both surfaces. So if that's the case, why do we also have this wide variety of dual-sport bikes, which range from street-legal dirtbikes to adventure-tourers? Wouldn't it be better to file the bikes under "miscellaneous"?
Fort Collins, CO
A Depends on which two sports you're most likely to find yourself in. The average supermoto derivatives are better suited to smoother surfaces-paved or unpaved-than their dual-sport counterparts, which may have to deal with whatever the trail serves up: rocks, logs, ruts, sand...you name it. Hence the supermoto bike's shorter suspension travel, lower center of mass, bigger brakes and wider wheels generally shod with sticky street rubber or even slicks. Dual-sport bikes run the on/off-road gamut from the Moto Guzzi Stelvio-happiest on rough pavement or smooth dirt-to the KTM 690 Enduro, which is essentially a dirtbike with lights and a license plate. You could survive an easy dual-sport ride on a supermoto bike, or skid around a go-kart track on a dual-sport. Just don't expect to have nearly as much fun as you would've on the purpose-built version.