The Service Dept

THE SERVICE DEPT

Len Vucci

If you have a question or comment of a technical nature, send it to us. We’ll attempt to answer as many letters as possible and we’ll publish those which we think are of interest to the majority of our readers. We’ll also print some helpful hints and how-to’s reflecting frequently asked questions. Technical correspondence should be sent to: Service Department, CYCLE WORLD, 1499 Monrovia Ave., Newport Beach, Calif. 92663.

A QUESTION OF TIMING

I read your article about ignition tuning in the October ’76 issue with much interest because I have recently been trying to figure out why my Suzuki GT380 runs fairly well at speeds up to 50 mph and terribly above that.

After checking both static and dynamic timing with no improvement, I was tempted to investigate carburetion. But first I asked myself, “How do I really know the points are opening at 3mm BTDC?” So I rigged up a top dead center indicator out of an old Twin Otter glow plug and a dial reading metric caliper, took out the spark plugs and hooked up my tone changing buzz box. I found I couldn’t get 3mm BTDC on the “left” points because the slots in the main breaker plate were not long enough. Hoping to be on the right track, I then removed the main breaker plate, leaving the wires attached. Then I lengthened the slots by punching out the metal with a Whitney Jensen metal punch, and dressed up the job with a small rattail file. Soon everything was back together and 3mm advance easily attained.

Well, I held my breath as I swung out the kick starter, turned on the key, saw the green light and gave her a kick. Zing-g, my Suzuki came to life like she never did before. She’s as smooth as silk all the way up to the point when I don’t care to go any faster. Incidentally, the timing marks are not lined up any more. They are only an approximation.

Ken Buzzell Auke Bay, AK

One negative side-effect of mass-production methods is the occasional “What you see ain’t what you got” problem. Those of you who experience similar problems may find a similar solution.

We do, however, caution that point gap MUST be correct before attempting to set timing. Improper point gap adjustment sometimes makes correct timing unattainable.

GOOD POINT

To accurately adjust the points on your Kawasaki Zl, use the eight-cylinder scale on any dwell meter. Hook up the red lead to the set being adjusted and the black lead to ground. Both sets of points should be adjusted to 26 degrees. To increase the dwell reading, decrease the size of the gap. To decrease the dwell reading, increase the size of the gap. Flexstone works great for cleaning points, and can be purchased from any Snap-on Tool distributor.

Michael R. Murrell San Antonio, TX

HONDA HEADLIGHT SWITCH

Your road test of the Honda CB400F criticized the lack of an on/off headlight switch. It should be simple to add a switch; however, a friend who is a Honda mechanic said he was told at Honda service school not to add a switch. The reason given was that the Honda charging system is designed with the constant load taken into account and that reducing the load results in an overcharged battery. This doesn’t make much sense to me because I assume the CB400F electrical system must contain an effective voltage regulator that would prevent overcharge.

I wish to add a switch because I would like to use a quartz-iodine headlight and don’t relish the thought of that expensive bulb burning constantly.

I would appreciate your comments on the effect of adding an on/off switch and whether you know of any quartz-iodine lamps that fit the CB400F.

J.A. Lynn Pittsburgh, PA

Although a definitive answer was unobtainable from American Honda Corp., we have yet to see an instance where installation of a headlight on/off switch has been detrimental to battery life.

We must mention that in most states, use of quartz-iodine or halogen lamps on-road is illegal. Additionally, where quartz lights are allowed, specific brands and models must first be given approval. In other words, one quartz-iodine lamp may be legal while a different quartz-iodine lamp may not.

Several manufacturers offer high-power replacements for conventional sealed beams. These can be obtained at most auto accessory shops. Basically, you will need a dual-filament (high/low beam) lamp rated at approximately 55 watts at 12 volts. Be sure to avoid the “pencil beam” pattern lenses—these have little or no dispersion to the sides. Ditto the super-wide dispersion lamps, for the opposite reason.

I’ve been reading and enjoying your magazine for several months now and you have mentioned several times about the new Honda’s full-time lights-on problem. I had my new ’75 CB500T only a couple of weeks when I cured that problem rather easily. Having ridden dirt bikes for some time, I realize the value of a kill button or switch. But on a street bike with a convenient ignition switch topside, who needs a kill switch?

I’m no electrician, but after studying the Honda’s wiring diagram I discovered that I could disconnect the kill switch inside the plastic junction box on the frame and reconnect it into the lighting system. 1 now have a convenient on/off switch for the lights without having to add an additional switch to clutter up the bars.

Don Aldridge Temple City, CA

This is an ingenious method to thwart yet another of those “for your own good” measures becoming much too prevalent of late. However, elimination of the kill switch is a trade-off which we’d just as soon forego.

Instead, installation of a simple toggle switch on the headlight shell is, in our opinion, a more acceptable alternative. The hot lead (black/yellow for most Hondas) going to the high/low beam selector can be cut, and the ends soldered to the toggle switch.

The fix for late model Suzukis is extremely simple. The on/off switch is still present, but the lever has been immoblized. Removal of the plastic lever reveals a cast-in tab which, when clipped off, restores a bit of personal freedom.

LEFT-HAND GAS THROTTLES

I am left-handed and own a Honda XL175. Do you know of any firm that makes left-hand gas throttles for motorcycles?

Paul H. Gallagher St. Louis, MO

We have not seen an aftermarket lefthand throttle. A Honda push-pull dualcable throttle (like that on the XL250) can easily be adapted. Simply hook your cable to the original “push ” side.

SUSPENSION FIX

I would like to improve the road holding capability of my ’76 Honda CB750F. I would appreciate hearing whatever suggestions you may be able to offer.

Being a rider interested in road racing, I also want to replace the rear shocks. What brands, models and spring rates would you recommend for one-up riding 80 percent of the time?

James W. Watson Fort Eustis, VA

Number One Products has recently introduced a Trickit (part number H750F-14) for the F.

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Rear shock spring rates, for a rider of 150160 lb or so, should be about 110 lb/in., with little or no preload. For heavier riders, slightly stiffer springs may be in order, or preload may be increased. The same holds true for two-up traveling.

As for the shocks themselves, in an upcoming comparison test in CYCLE WORLD, we'll reveal not merely advertised specs, but actual performance of the manufacturers' latest offerings.

TENSION HEADACHE #520

I own a Kawasaki F9 Enduro bike that rapidly loses its proper chain adjustment after riding. The drive chain becomes too loose and flaps strongly when running.

I want to fit this machine with a springloaded tensioner to keep slack out of the chain. I’m referring to the type found on many motocross bikes that have long travel suspensions. Do you know of any companies that sell a tensioner which would bolt on to my bike?

Glen Pickle Nashville. TN

Sounds to us the problem you're experiencing is the result of an excessively tight chain. When a chain is properly adjusted, a slight bit of slack is necessary to compensate for the tightening effect as the rear suspension is compressed. When over-tightened, the chain is subjected to tension forces from rear suspension movement. These forces are much greater than those from normal acceleration/ deceleration. Besides contributing significantly to premature chain failure, an excessively tight chain tends to limit rear wheel travel, yielding a harsh ride.

Should installation of a new chain be necessary, don’t neglect the sprockets. A worn sprocket will swiftly turn your new chain old.

If you’ve kept the chain well lubed, and the above-mentioned conditions do not apply, a tensioner may be the answer. There are severed on the market from which to choose. From personal experience, we recommend the tensioner from Up-Tite Products, 10261 Halawa, Huntington Beach, CA 92647.