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.
THAT’S THE BRAKES
I’ve been considering trying to fit my 1979 Honda CX500 Deluxe with dual front disc brakes. I think it would look great, so if it would improve braking just a little. I’d be willing to do it, realizing it will cost around $300 in parts. It seems like a disc plate would bolt right on to the right side of the wheel and my brake cylinder is the same one as is used on the GL1000 and CB750F. There’s a custom shop nearby that says it could weld a bracket onto the right fork slider. While I’m at it, I think I’ll have the discs drilled out, install braided stainless steel, brake lines and put air caps on the forks. My questions are 1) Would this improve braking performance? 2) Would the extra unsprung weight adversely affect handling? 3) What do you think of the idea?
Eric Norby Richmond, Virginia If the entire project went well and there were no problems, you might gain a little braking power. The additional unsprung weight would adversely affect handling, though not enough to be a big problem. In general, we would recommend against the project. Now the explanation.
Welding a bracket on the fork slider is not a good idea. The heat from welding could warp the slider, causing a problem with suspension action. If you must have dual front discs, find a set of forks with integral brackets for the second disc such as those on the CB750F. The braking power of the stock CX500 is likely as good as most riders are capable of using. There is no big shortage of braking power on the bike. If you must have greater braking power, a better way to go would be with improved brake pads such as the Ferodo pads available from PRO (P.O. Box 445, Frafton, Mass. 01519) or Tom Hayner's Racer's Supply (6959 Van Nuys Blvd., Van Nuys, Calif 91405). Air caps or stiffer fork springs would be a good idea if you frequently try maximum braking effort because the soft stock fork springs will allow the front end to bottom under heavy braking. Drilled discs won't improve braking power, but will lighten the disc for less unsprung weight.
HARD CHARGING
Help—I have a 1979 Yamaha 1100 Spe-> cial with battery problems. The dealer is super in his efforts, but I still have a bike with a so-so battery problem.
I have outfitted the bike with Bates bag^ (with lights) a Wixom fairing with side and front running lights. I have hooked up two, small sealed beams in the high beam circuit and one set of yellow running lights in with the low beam circuit. At night the quick flashing from upper beam to lower' beam is very distractive to “sleeping” auto drivers.
I also have a radio wired to the accessories circuit which is provided. With all lights on low beam, the total draw (with radio) is 17 amps. On high beam, turn signals on and brake lights on, the total draw is 28 amps. The dealer has checked the system and replaced the original bat-* tery. They could not find any irregularities in the system including my additional lights I hooked up, with a minor exception of a 0.1 amp draw in the radio when the radio is off.
I had a Honda 500 Custom and a Gold Wing dressed in the exact same way and* never had any problems with the battery. I wonder why I am having this problem with the Yamaha 1100? Oh yeah, the second battery has eventually run down also. One thing I’ve noticed, when starting the bike it, seems that the battery doesn’t produce a high rpm in turning the engine to start, as in other bikes I’ve had.
So I wonder if there doesn’t appear to be? anything on the surface that drains my battery, can it be that there’s an unusual' thing happening within the starting system itself that is creating a big drain on the bike. It seems that if I make a lot of starts, and stops for a continuing time, without any long runs in between, the old battery, just eventually won’t fire the bike up.
Kenneth Williams
Montgomery, Alabama
Several problems are involved in your battery trouble, none of them big enough to be the single cause but all of them together becoming more than your battery and^ charging system can handle. Starting with your alternator, it 's capable of generating a-* maximum of 27 amps if it's in top condition and the engine is running at a high enough speed. Because the XS1100 has such enormous torque, it doesn 't have to be revved up as high as your Honda 500 or even the Gold Wing you had. The Yamaha has to be revved up to about 5000 rpm to generate maximum power and at lower speeds the output is far lower. Without the auxilliary equipment the Yamaha charging system can equal the draw when it's running at about 1500 rpm.
Now consider the battery. It’s a 20 amphour battery which is certainly large enough* to handle the stock motorcycle and some accessories but here you've got as much electrical draw as an automobile and a" battery only one-third the size.
Next look at the radio. It's probably designed to be installed in a switched circuit^ that is, wired through the ignition switch so that when the switch is shut off there's no¿ way power can go to the radio. Run directly from the auxilliary plug, the radio is drain-'* ing a small but constant amount of current, probably for a light or to keep the chassis'4 hot so it will turn on instantly. Before you can hope to solve your problem you should install a switch in the line going to the radio^ to shut power off completely.
Even your calculations on the total power _ draw may be a bit low, which would underestimate the problem. There's also the igni-^ tion taking a couple of amps and when the starter is used, it draws down the batterf even more.
It's no surprise that your battery runs down when the bike is usedfor short trips. Ij\ you must have all the lights running all the time, you can help keep the battery up to* snuff by putting a switch on the line to the radio and getting a trickle charger so yoM can charge the bike when it's not in use. A quick-disconnect fitting can be added so the* charger can be plugged into the bike without having to gain access to the battery. Some* motorcycle dealers sell trickle chargers withi the quick-disconnect fittings included.
There is another technique a lot of touring riders use. If you run a cigarette lighter fitting on your bike, directly from the ban tery but with a fuse in the line, it can be used not only to power accessories like radat* detectors, electric suits, air pumps and radios, but you can charge the battery by4 putting an appropriate fitting on the end of ' the trickle charger.
POWER FOR THE DT100
I own a 1978 DTI00 Yamaha, which runs fine, but I would like more power. 1 was wondering if there was any way tc* modify the exhaust system or carburetion to give more power without harming thei engine.
Paul Crawford Greenville, Ga.
The simplest way to improve performance on the DT100 is to do a light cleanup on theM porting. The separations at the bottoms of the transfer ports can be filed to a sharp edgefor better flow; and the intake and exhaust flanges should be properly aligned and de** burred to eliminate steps and rough spots. Port shapes and heights at the cylinder waft are best left alone; a few mistakes with a file' can drastically reduce horsepower.
We don't know of anyone who currently produces a power exhaust or expansion chamber for the '78 DT100. However; you r^cin restore a good deal of lost power—and keep the neighbors happy at the same time— U?y replacing the stock baffe if it is missing. The DTruns best with the baffe in place. A klarger curb will also improve performance, though at some cost in time and experimentation finding the right jetting for the 100.
TOWING WITH THE GS
I am planning a trip this summer on my 1978 Suzuki GS550 and I would like to pull a trailer. Several of my friends have told me it is illegal in some states to pull a trailer with a motorcycle. I would appreciate any information you can give me on which states do not allow this or how I can obtain this information.
1 am also wondering about the relationship of trailer weight to body weight on engine strain. Is there more strain on the engine pulling a 100 lb. trailer or carrying Ü 100 lb. rider? If so, what changes or precautions can I take to avoid any unnecessary strain on my motorcycle?
Norm. Koster
St. Anne, 111. 60964
Moving 100 lb. of weight from the back of a motorcycle to a trailer will reduce the load on tires and suspension components and cure some of the weight distribution imbalance that can cause handling problems on the bike itself. However; the added rolling resistance from trailer bearings and tires, as well as the added wind resistance, will increase the strain on your engine and drive train. A Iso, it is impossible to move ¡00 lb. from a motorcycle to a trailer and still çnd up with a 100 lb. load because of the added weight from the trailer and hitch. A -light weight luggage trailer will generally weigh over 100 lb. empty; others go as high as 400 lb. A good hitch, which should be mounted on the frame rather than the swing arm, is also heavy. So the 100 lb. load, moved from the bike to a trailer; becomes a 200-300 lb. load j'or the engine, drive train pnd brakes to contend with.
The GS550, while it can probably pull a -trailer; is not the ideal bike for the job. But, if it is used j'or towing, it would be a good dea to change the countershaft sprocket, or both sprockets, and gear the bike down for highway cruising. The GS has a roller bearing crank which would rather rev than be heavily loaded at low rpm. If you are travling solo and not really strapped for space, a tank bag and carefully arranged load in ■saddlebags and on the passenger seat would go easier on the engine and make the bike *sajer and less cumbersome to stop. We haven't heard of any laws against motorcycles pulling trailers._
