Service
SERVICE
We welcome your technical questions and comments, and will publish those we think are of interest to our readers. Because of the volume of mail received, we cannot return any personal replies. Please limit your "Service" letters to technical subjects only, and keep them as brief as possible. Send them to: "Service," CYCLE WORLD, 1499 Monrovia Ave., Newport Beach, Calif. 92663.
HIDDEN SHIFT
About the October. 1978 CYCLE WORLD article by Dain Gingerelli, “Shift Detent,” I have the problem. Now give me the answer. How do I find it on a 1976 Honda CB550F?
John Kealoha Lahaina, Hawaii
It’s behind the clutch. You'll have to remove the clutch cover and clutch to get to it.
GETTING THE LEAD OUT
Recently I have been hearing that by Oct. 1, 1979 the amount of lead allowable in gas will be drastically reduced. The net effect of this will be that there will no longer be any premium gas, excluding Amoco unleaded premium which some bikes will not tolerate. I am, for better or worse, a Ducati enthusiast and as you are no doubt aware, Ducatis as well as most other European bikes still require leaded premium gas. Are these manufacturers
making plans to convert their bikes over to low or unleaded gas in the near future?
I realize that modifications can be made to permit the use of low or unleaded gas but this is usually at the expense of performance and a certain outlay in cash.
Ken Richter Topeka. Kansas
You're right about the amount of lead decreasing in premium gasoline. However, a number of oil companies have plans to introduce unleaded premium gas, similar to Amoco premium. It’s still possible to produce a low-lead premium with other additives to increase the octane rating. At this time it isn't known whether any oil companies will introduce a low-lead premium. Whether a Ducati or other high compression motorcycle can operate satisfactorily on a low-lead or no-lead premium is, at this time, an unanswerable question. Even if the octane rating of an unleaded gas is high enough to avoid preignition, the lack of lead in gasoline could contribute to shorter valve life.
In general, it is possible to increase the thickness of the cylinder base gasket of a motorcycle enough to lower compression so that low octane gasoline can be used. BM W offers low compression models in European markets which use the thicker gaskets. Yes, performance does suffer. The same modifications can be made to motorcycles other than BMWs.
According to Seth Dörfler at Berliner Motor Corp., the Ducati factory is aware of the impending changes in gasoline and is working on changes. Dörfler said there is no date set for a changeover, however.
A ¡though the usual route to making a low octane engine is to lower compression, the tv's more to it than that. Witness the Honda CX500 which has a 10 to 1 compression ratio and runs fine on unleaded gas. Cam timing, combustion chamber shape and ignition timing all play a part in the design.
For those who demand the power of a high compression engine, there are alternatives.
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Aviation fuel can be purchased from many smalt airports and may work better for some engines. There also are octane boosters which can be added to gasoline to raise the effective octane rating. And there's alcohol, which is a fine fuel. For information about running alcohol in a bike, read "Burn Booze In Your Bike" in the August, 1978 CYCLE WORLD.
LOOKING BACK
I own a 1978 Kawasaki KZ1000Z1RTC. Previously I had a 1976 Kawasaki 900 LTD and both bikes had the same enigma. At certain engine speeds the mirrors would vibrate. This happened mostly above 5000 rpm and would render them not only useless, but the sound was rather annoying.
To cure this problem 1 removed the mirror heads from their stalks and then removed the mirrors from the plastic caps. Inside the caps are molded bosses which the mirrors snap into. After cleaning both the caps and the mirrors with denatured alcohol, 1 tilled the bosses with a 3/16 in. layer of RTV (silicone sealer) and let it set up for half an hour. I replaced the mirrors in the caps. When remounting the mirrors onto the stalks, I placed a 3/8 in. rubber Tiring over the thread between the tightening nut and mirror head. After adjusting the mirrors and letting the silicone sealer cure for a few' hours, it was ready to go. It has worked verv well.
Douglas Seberle Bayshore, N.Y.
TIRED TIRES
I recently purchased a used Honda CB550F equipped with the stock Bridgestone tires that show very little wear (fine rain grooves still visible). The problem arises with the loss of traction when cornering. This slipping occurs well in advance of peg scraping, which seems premature. In addition, your August tire test issue rates the Bridgestone as a “good” cornering tire. I’ve checked and varied the cold tire pressures within the limits Honda provides with worsening effects. What could be causing my premature tire slippage1?
James Chin, Champaign. 111.
One bit of information you didn 7 include was the year model of your motorcycle. If the tires, as indicated, are original equipment, they could be several years old. Even two-year-old tires will have hardened some, losing traction. The rubber in tires is affected by age and by chemicals in the air which can harden the rubber.
Don't expect original equipment motorcycle tires to work as well cornering as the tires tested in the CYCLE WORLD tire> test. The test tires were all high performance models offered from each of the tire companies, not the models sold as original equipment. Bridgestone supplied the Superspeed model, which they felt was their best performance tire. Motorcycle tires also have been improving and the best tires available today are superior to the best tires available three or four years ago, generally.
If cornering traction is important to you, consider installing new tires.
RD400 TIPS
I can sympathize with the frustration of the RD400 owner who wrote in with the problem of stumbling and refusal to rev after around-town riding. I’m on my second RD (a 250 and a 400C which I’ve had since new) and can suggest a cure. Raising the needles one notch helps very slightly, but drops mpg by 2 or 3. Try going on an exclusive diet of unleaded gas. Since I took this route, the problem disappeared and I’ve been getting much better plug life—I can go a year on a set of plugs.
For what it’s worth, I also run Klotz twostroke oil exclusively, although I can’t say whether or not this is a contributing factor of my success with my RD400.
This machine has given me three years of trouble-free service and has everything I want in a motorcycle. A used RD400C goes for around $7-800 here and I would recommend one for someone looking in the 400-500cc class.
Jim Kline Blue Bell, Pa.
MORE BITE FOR THE KL250
I’ve read that the Kawasaki KL250 experiences front end washout in sand and across whoop-do-doos. Is this due to the bike’s rake? And can it be cured by 1) air caps for the front forks, or 2) a larger front tire?
Also, would an accessory pipe be lighter than the stock one and would there be a gain in power to bring the KL250 into line with the other four-stroke road/trailers, i.e. XL250, SP370, XT500?
A new KL250 is almost $500 cheaper than the Honda and others here in Australia. If I spend the money on accessories, would I end up with as good or better a bike?
A. Johnstone Queensland, Australia
We'll have to narrow some definitions. Any motorcycle will push the front wheel in sand and have trouble over the whoops. It’s just that some bikes get this at lower speeds than others, and just about any dual-purpose bike will lack the offroad precision of just about any pure dirt bike.
We haven't done much with the KL250, but one of our guys has been working for several years with an early XL250, which is just about the same basic design.
Losing the front end in sand, that is, deep sand, is caused by the heavy front end and relatively narrow tire. If local conditions and laws permit, a knobby front tire will make the front more stable, and a wide knobby works best of all. Our man runs a 3.50 x 21 Cheng Shin enduro tire and says it’s the best single change he’s made. Failing the knobby, look for a 3.25 or 3.50 trials tire.
You can improve front end bite by increasing the rake and the easiest way to do that is to fit a longer pair of rear shocks. Another inch in the back will give another degree in front and won’t (in our experience, at least) reduce straightline stability significantly.
An aftermarket exhaust will be lighter and will add power, but unless you do a complete racing conversion, the KL250 engine will never match the power of the XL250 or the Suzuki 370 or Yamaha 500. If you want speed, you’ll simply need a larger engine, and if you want motocross handling, you’ll have to buy a motocross bike.
What the KL250 will do is provide fun off road and reliable transportation.
YAMAHA XT500 CARBURETORS
I am considering a carb swap on my XT500 Yamaha but can’t decide which brand to use. Everyone gives me a different answer about which is best. I lean toward the El kit from AÍ Baker R&D but my dealer says Lectrons and Els are hard to tune at this altitude. Also, would a CDI ignition be beneficial?
Steve Morgan
Larkspur, Colo.
The Yamaha 500 4-stroke engine will produce more horsepower with almost any larger after market carburetor. We have tried 36/38mm Mikunis, 36mm Lectron, 36mm El, and a 36mm Dell’Orto. All give more power when properly tuned. All are available with the jetting close when bolted to a stock engine. If other engine mods like cams etc. have been installed, carburetor jetting can bé a hassle. The Lectron and El style carbs are different to tune, and may require more fiddling before they are spoton. Tuning for your altitude shouldn ’t pose a problem with any of them. A CDI ignition will eliminate point maintenance and furnish a hotter spark.
