Service

SERVICE

Faulty Vision

I took Yamaha up on one of their $1700 Visions after three years away from cycling to finish school. I can deal with the flat spot in the carburetion, but I really would like to make the bike handle better. With the preload set to its softest setting, the bike bucks and wiggles (not wallows) when leaned over hard. Any suggestions for improving suspension? Are the stock Bridgestones at fault? J. Clark Stivers Bar Harbor. Maine

A multi-step approach to improving handling is advisable. First, better tires would be in order. Metzelers in 100/90-18 (front) and 110/90-18 (rear) sizes would be a reasonable choice, but not necessarii v the only option. After that, the next investment would be a better rear shock. There aren't many dampers that fit, so you might have to use the very good, but expensive, Fox unit (available through Moto-X Fox, 520 McGlincy Lane, Campbell, CA 95008). Next, some improvement can be had by stiffening the Vision 's fairly flexible front fork with the addition of a fork brace. Finally, add a steering damper to steady the Vision 's steering under extreme conditions.

Hot coils

I presently own a 1980 GS 1 100E and I want to improve its performance without spending a fortune. One of the things I had in mind was to change its coils to high-output coils. My dealer says that it won’t help but instead will hurt the engine due to piston pitting caused by excessive heat. I understand that OEM coils don’t put out enough to adequately sail a bike down the road. Who is right? John Jefferson Midwest City, Oklahoma

Certainly not your dealer. Unless you substantially change the sparkplug gap, combustion speed and temperature won 7 be affected b y a coil change. Unfortunately, neither will power. Higher-output coils can make a motorcycle easier to start and more tolerant of carburet ion errors, but current original-equipment coils put out enough spark to start the mixture burning, and that's about all that's required to make power. An extremely powerful ignition system used in conjunction with an .080-inch or greater spark gap and less ignition advance ma y offer some power and economy benefits, but that kind of ignition energy requires more than a coil swap to achieve.

Nitrous pipe dreams

I am the owner of a 1984 GS550ES Suzuki and was wondering if the addition of FI mufflers would increase my performance. Also, I would like to know if the application of nitrous oxide would have any adverse effects on my engine or if any modifications would be needed. I asked my dealer about this and he told me to write you. Kevin Hilliard Palm Bay, Florida

FI mufflers are offered mainly for looks, and for having a lower price than stock mufßers. By FI 's own claim, and our own experience, FI mufflers don 7 have a significant positive or negative effect on engine power.

Nitrous oxide, however, can give you the greatest power boost of almost any single modification. Nitrous oxide, carried as a compressed gas and injected into the intake tract, breaks down in the combustion chamber. The breakdown adds oxygen to the existing air/ fuel mixture, effectively convincing the engine it's much bigger than it is.

More fuel must be added to balance that oxygen, so a fairly sophisticated system that combines nitrous injection and mixture enrichment is required.

There are problems, however, with nitrous oxide as a power booster. To start with, a bottle of compressed gas that can be conveniently carried on a motorcycle contains only enough nitrous for a few seconds to a few minutes worth of additional power.

Besides that, the power boost will increase temperatures and stresses inside the engine, perhaps leading to serious reliability problems. Still, a nitrous injection system can be a useful tool for making a bunch of horsepower for a short burst of speed.

Less dual, more purpose

I recently purchased a new 1983 Honda XL600R. I have been extremely pleased with its performance on the road, but have had considerably disappointing experiences when taking it into the wilds due to its ungainly weight, its limited traction with the stock tires, and its road-biased gearing.

In addition to the 600’s inherent problems (which are especially noticeable in loose sand), I have probably made things worse through my efforts to tune the suspension. I simply don’t have enough expertise in that area to adjust my shock and forks for a person of my 135 pounds. However, I feel I have made adequate compensation in the drivetrain department by dropping two teeth on the countershaft sprocket.

What adjustments or alterations can I make on my bike—short of trading it in—to improve its off-road performance characteristics? Mark H. Barnes Deland, Florida

Knobby tires would offer the biggest improvement in offroad performance. The Bridgestone dual-purpose tires that come on XLóOOs are biased toward pavement riding, and work far better at that than they do off-road. Our testing has found that most bikes as heavy as the XL600 work best offroad with a 3.25x21 Met zeler on the front; any 17-inch knobby that will fit, including a stock XR500 tire, will be an improvement on the stock rear tire. Understand, of course, that the streetability of the bike will be compromised with knobbies, and that they might even be illegal.

As far as suspension tuning goes, all the tips that appl v to normal dirt bikes also apply to the XL600. Start with Honda's recommended oil level and air pressure in the fork, and adjust the rear spring preload so that the rear suspension compresses about 23A inches from the fully extended position with you sitting on the bike. Start with the shock damping adjusted to the position recommended in the owner's manual, as well. Those settings should be a reasonable baseline for further modifications; for a complete adjustment procedure see the suspension tuning article in the August, 1983 Cycle World.

Rare sparkplug

I own a 1979 Suzuki DS80, which has an NGK B7ES sparkplug in it. The plug should be replaced, but the only replacement guide in the owner’s manual is for NGK and Nippondenso. These brands aren’t available in my country any more, but a Bosch sparkplug can be found easily. The only trouble is that I don’t know what number and type of Bosch plug would have the same heat range as NGK’s B7ES. Could you help? W. Gharibian Tehran, Iran

The Bosch equivalent to a B7ES is a W42C.

Combustion controversy

I have a doubt about something that appeared in your “How Motorcycles Work” article about fourstroke engines. The article said that the piston is forced downward by the heat generated during combustion, which raises the temperature and so the pressure in the cylinder.

That’s what I find hard to believe. Combustion is a chemical reaction that starts with air and fuel, and produces waste gases that are definitely not air. So isn’t the piston pushed down by the raised pressure caused by the bigger volume of the gases produced by combustion, and isn’t the heat generated only the inheritance of this? Marcelo Siqveira Gios Sao Paulo, Brasil

The number of molecules making up the products of combustion is only 5 to 10 percent greater than that of the air/fuel mixture before combustion. Since many of these freshly created molecules are water, there is little difference in the volume of the stuff in the cylinder before or after the spark goes off, if only the temperature were the same before and after. It's the heat generated by combustion that raises the temperature, and, therefore, the pressure, and makes the engine work. The change in composition of the cylinder contents has ont y a minor effect on the whole process. Theoreticians don't call internal-combustion engines heat engines for nothing.

Aermacchi spares

I own a 1972 125cc dual-purpose Aermacchi/Harley-Davidson. Could you give me any clue as to where I could get parts and information on the engine? Are there any compatible parts I can use? Robert Amico Hollis Hills, New York

Parts might be available through Cagiva. You could try a Cagiva dealer, if you can find one, or contact Cagiva 's U.S. offices: Cagiva North America, Inc., 2300 South Normandie Ave., Torrance, CA 90302; (213) 538-9337. Cagiva bought Aermacchi from Harley-Davidson several years ago, and still produces some small motorcycles that are direct derivatives of Aermacchi models. If nothing else, Cagiva might be able to supply engine parts for your bike.

Lazy oil light

I have a problem with my ’82 900F Honda that no one seems able to diagnose. When I start the engine cold, the oil-pressure light stays on about three seconds. When the engine is warm, the light goes off sooner. If I shut the engine off and restart it fairly soon thereafter, the light goes off immediately. It has been doing this for about 1000 miles.

The bike sees redline on a regular basis with no problems whatsoever. I can detect no ill effects of this curious problem, and all the mechanics I have spoken to tell me not to worry about it. The problem doesn’t seem to be getting any worse, but it never used to do it at all. The light used to go out instantly. I have been running Golden Spectro synthetic oil, and some have said that the problem may be caused by this oil draining back into the pan more quickly. What could be causing this, and is it dangerous? Should I ignore it? AÍ Stern Dayton, Ohio

II would seen] that for once, all those mechanics are right. The problem indeed is no problem at all, and is caused by the oil draining hack into the sump once the engine is turned off. When the engine is cold, the oil is thicker and takes a little extra time to get pumped from the sump, through the various oil galleries, and to the oilpressure sending switch. When the engine is warm the oil is thinner, and so the pumping time is reduced. And the reason wh y the light goes out immediately when the warm engine is restarted fairly quickly is that the oil has not had much of a chance to drain awa r from the sending switch, whereas a cold engine has had considerable time to let the oil drain away.

You did not, however, state the weight of the oil you are using. If the oil is a heavier grade than that recommended by Honda, it could result in the slow action of the oil-pressure light. But assuming that you don't have the wrong-grade oil in the engine, the “problem " won 7 cause an v engine damage so long as you don 7 rev the engine highly while the light is still on.

Frustrated flasher

I recently installed two driving lights on my 1980 Honda GL 1 100. Each light has a 55-watt halogen bulb in it. At night when I run with my stock headlight and both driving lights, I'm using 165 watts of current, and the battery does not seem able to hold this amount of wattage. When I apply the brakes and use the turnsignals at a traffic light, there isn’t enough power to operate the flasher, so it stops clicking. I've had my battery checked and have been told that it’s fine. Can you help me with this problem? Don Pittillo Rolla, Missouri

This condition is not all that uncommon on motorcycles that have been equipped with high-wattage accessories. The problem lies not specifically with the battery itself, but with the fact that at lower rpm, the battery has a negative current flow— that is, more current is being drawn out of it by all of the electrical components than is being put back into it by the alternator. The alternator on your bike is rated at about 300 watts, but that rating is at 5000 rpm. Below that engine speed, the alternator output is roughly proportionate to the reduction in rpm. So while the alternator can 7 be putting out much more than 60 or 70 watts at idle, all of your electrical components are drawing in excess of ^200 watts. With such a huge drain (¡40 watts, or 11 amps) on the batV tery, its available voltage quickly drops to the point where certain components won't work.

Installing a larger battery (if you could find room for it, which is doubtful) would only delay the onset of the problem for a short period each time ^ you stopped or slowed. And installing a higher-output alternator is no solution, either; for one thing, all G LI 100s have a 300-watt alternator, and the 360-watt unit from the G LI 200 won't ^ fit the 1100. Ánd even if you could somehow adapt the 1200's alternator , to your bike, the low-rpm output wouldn 7 be increased enough to produce a positive current flow through the battery while you're stopped at a light.

Your best solution, then, is both simple—and cheap; Install a switch in ^ your driving-light circuit so you can turn those lights off when you're just piddling around in town. You really don 7 need all that candlepower when you 're sitting at stoplights, an ywa y. But if you insist on using the lights at all times, ride a gear or two lower in low-speed situations than you nor" mall y would so the engine is spinning up near 4000 rpm, which is what it will take to prevent battery discharge. And if you don 7 find either of those proposals palatable, at least rev the engine up to 3500 or 4000 rpm while you 're sitting at a traffic light to help keep the battery charged.