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.
SUZUKI WOBBLE
I was particularly interested in Herb Abell’s letter to Service in the December issue regarding a high-speed wobble problem he encountered with his 1982 GS1100E Suzuki when he switched from the stock OEM tires to Dunlop Sport Elite tires. I own a 1982 GS750E and encountered the same problem when I switched to Sport Elites.
Though you do give a good rundown of troubleshooting the problem, the cause is indeed the Sport Elites. The wobble with Elites is most pronounced accelerating out of fast corners or coasting with hands off the handlebars (scarey!).
Not wanting to sacrifice the cornering power of the Elites by having to switch back to a lower performance tire, I set about trying to solve the front end wobble. A CC Products fork brace stiffened up the front end and made it more responsive, but the wobble was still there. What solved the problem completely was an adjustable steering damper kit from Racer’s Supply. Handling was so vastly improved even over stock that I’d recommend the installation of a damper to anyone with a stability problem. Even in everyday use the bike is now oblivious to rain grooves and pavement joints, making it much
safer and enjoyable to ride in all instances.
As you pointed out, many times a handling problem like wobble can be traced to bad shocks. And since I coordinate the Superbike road race program at Moto-X Fox, I wish I could recommend a set of Fox Shox as being able to correct the Suzuki GS’s handling problem with Elites. And while our shocks will improve overall handling even more, in this instance it’s the steering damper that solves the wobble problem.
Jim Gianatsis Moto-X Fox Campbell, Calif.
Steering dampers can help solve some handling problems, and, as you surely know, no high powered road racer can be found without one. These days even many flat track racers are equipped with steering dampers. A hydraulic steering damper seems to be most effective in controlling front end wobble, and may not necessarily have much effect on cornering weave, so it’s no handling cureall.
The addition of a steering damper would be worth trying when an otherwise unsolvable handling problem presents itself, and should be a worthwhile addition on any motorcycle. For other readers who would like to try this fix, the
address of Racer’s Supply is 6959 Van Nuys Blvd., Van Nuys, Calif. 91405,
phone (213) 781-6386.
MOTORCYCLE TOOLS
I really enjoy riding and tinkering with old motorcycles. However, I need some information. Who is the major supplier of motorcycle tools in the United States? I can’t find anyone who specializes in this line. Where do bike shops buy their tools? None of them in this area will tell me.
Here’s one example of my needs: there must be a better way of timing my old Bultaco than with a degree wheel. I want a dial indicator! I heard last summer that some manufacturer offers one with a digital readout, i.e. 8° TTDC. Can you help me?
Charles S. Howland
Columbus, Ohio
If by motorcycle tools you mean the hand tools used to work on motorcycles, Sears and Roebuck may well be the largest supplier. We suspect that you have something more specialized in mind and for these more specific tools you have to look to other sources. Rocky Cycle Co., 1250 Elko Drive, Sunnyvale, Calif. 94086, distributes a wide line of general use motorcycle tools, including such things as chain breakers, flywheel pullers, carb synchronizers, and, yes, dial indicator sets for ignition timing. These can be ordered from Rocky by your local dealer or accessory store.
Another source of useful tools is your local Snap-On Tool distributor, who should be listed in your phone book. While Snap-On is basically oriented toward automotive and industrial business, it does offer just about anything you need to work on any engine or device. Besides, the several hundred page Snap-On tool catalog can keep a tool junkie entertained for days.
The motorcycle manufacturers themselves are the only sources for the most specialized tools. If you need the tool that locks the clutch hub of your CanAm 250 in place, you better see your Can-Am dealer. Likewise, the only person likely to have the tool designed to rivet Honda CB450 cam chains is your Honda dealer. Almost all special tools can be ordered through your local dealer, but they often tend to be pricey because of their limited production and distribution.
As well as selling these extremely specialized tools, many of the manufacturers offer more general interest motorcycle tools as well. Dial indicator timing sets are available through Suzuki, Kawasaki, and Yamaha, and Yamaha offers a low range ohm-meter that’s useful ^ in setting timing on two-strokes. The Japanese manufacturers with the exception of Honda list their tools in separate catalogs or micro-fiche cards, and you should be able to look through the range at your local dealership.
Finally, we’ve never heard of anyone offering a digital readout dial indicator for motorcycle timing use, but that doesn't mean one doesn’t exist. From our experience it would be an answer to an unasked question, as conventional dial indicators are perfectly satisfactory.
LAWSON SEAT?
I own a 1982 Kawasaki GPz550. I would like to know if the low cut seat on the KZ1000R Eddie Lawson Replica will fit, or can be modified to fit, on the 550.
Mike Henson Grand Jet, Colo.
The seat from the KZ1000R will not fit on the 550. However, Kawasaki, through its accessory division, offers a similarly shaped seat specifically for the 1982 GPz550. This seat differs from the Eddie Lawson Replica seat in having red trim instead of being completely black. The part number of the accessory seat is K53001 -122, and it can be ordered by any Kawasaki dealer.
FRAME DESIGN
Do you know of any books or material on the design and construction of motorcycle frames? If you do, would you send me a list of the titles and authors? Any help you can give will be much appreciated.
Carl Gossard Eureka, Calif.
The only book we know of that diq rectly discusses motorcycle frame design is Phil Irving’s Motorcycle Engineering. Written in the late 1950’s, this book is not completely up to date. However, it does give a good overview of the subject, and discusses frame and suspension arrangements other than just those currently fashionable. Another valuable work is the compilation of technical papers presented in Motorcycle Dynamics and Rider Control, published by the Society of Automotive Engineers. These papers approach motorcycle handling from the analytical, math-model side, and offer useful background information rather than construction details. Racing and Sports Car Chassis Design, by Costin and Phipps, discusses race car construction practices from the 1950s and early 1960s, when (before the wing) race cars and motorcycles shared some of the same chassis problems. A final book recommendation would be Aircraft Structures by Peery, or one of its equivalents. This is an engineering text written to teach structural analysis to aeronautical engineering students, and requires some physics and math background to be of much use. All four of these books are available from Classic Motorbooks, P.O. Box 1, Osceola, Wise. 54020.
An important thing to realize is most motorcycle frame design is still more empirical than analytical. Read what can be found on the subject, study what other people are doing, and don’t hesitate to try out your own ideas. The subject is not so thoroughly documented that you can learn everything about it by referring to the right books.
GPz PIPE AND FILTERS
I own a 1982 GPz550. I want to put a Kerker pipe and K&N air filters on it, but I have been unable to find jets for the carburetors.
The carburetors have three jets per carburetor. Do you know where I can get jets for them and do you know how to jet such a carburetor? If you know of anyone that has already done this, I would appreciate knowing what jet sizes he used. I also would appreciate the address of anyone that has larger jets. If no jets are available in the U.S., how about Canada?
Roland P. Middelraad
Las Cruces, N.M.
The TK constant velocity carburetors used on the 1982 GPz550 have the worst parts availability of any current carburetor. Because of this, we would strongly recommend that you be very careful in making modifications to your motorcycle. From our experience with other motorcycles, we would expect that you could run a 4-into-l pipe with a quiet baffle without rejetting. However, we haven’t actually tried a Kerker pipe on a GPz550, so we can’t guarantee that rejetting will not be required. One thing we are sure of, though, is that if you remove the stock airbox and install individual air filters, drastic changes will be required.
The only people working with the TK carburetors for racing uses are at Champion Moriwaki (1980 Harbor Blvd., Costa Mesa, Calif. 92627, phone (714) 642-2040). They have discovered that one style of Mikuni main jet will interchange with one of the two main jets used in the TK carburetors. Other than that, they carry the stock sizes for the other jets, so they can be drilled out to larger sizes. Champion also carries Canadian model jet needles, which have the multiple grooves for different needle positions that are only a fond memory in he U.S. Even though Champion foriwaki does carry these carb tuning rts, their recommendation for street is to keep the stock airbox in place.
750F RUBBER MOUNTS
Is there any way that the engine mounting system of the CB900F can be adopted to the 750 models? My girlfriend is always complaining that her feet are vibrating at cruising speeds (5560mph). I’ve tried to put rubber washers in some of the mounts with only marginal success.
Also, for all those 750F owners who •think their seat is too hard, the 900F seat will bolt right on. It gives untold hours of comfort while maintaining the Super Sport appearance.
Rich Warner Colonia, N.J.
There is no practical way to use the 900F rubber engine mounts on the 750. Both the frame and the engine cases are different, and the cost of switching parts around would probably be more than trading up to the 900. Perhaps you could reduce the vibration reaching your passenger by installing softer passenger peg rubbers, or by continuing to experiment with rubber mounting the entire foot peg bracket.
KAWASAKI Z-2 PISTONS
I am the proud owner of a 1975 Kawasaki Z-2 750, a Japanese model that was never imported to the U.S. as far as I can tell. Does any company make pistons for this model? Information for my bike is hard to come by as most Kawasaki dealers have never heard of a Z-2! I have heard that the 900 cylinder and pistons will fit, to make a short stroke 900. Is this possible? Any information would be very helpful.
Kenneth J. Bychak
Morgan Hill, Calif.
The Z-2 was a short stroke version of the Z-l, with a 2mm smaller bore size. (Bore and stroke of the Z-2 was 64mm x 58mm, compared with 66mm x 66mm for the Z-l). The cylinder head and deck height were the same for both engines. This was possible because the shorter stroke Z-2 crank used proportionately longer connecting rods. So the Z-l cylinder and pistons could be used on Z-2 cases, but the 106cc combustion chamber volume that gave an 8.5:1 compression ratio on the Z-l would only yield a 7.5:1 compression ratio in the resulting 794cc engine. This compression ratio is too low for a good performing engine, so this isn’t a recommended modification.
A better choice would be to use a Z-l cylinder with 70mm, high compression pistons available from Action Fours (1517 E. McFadden Ave., Santa Ana, Calif. 92705, phone (714) 541-5341). These pistons were intended to enlarge 903cc Z-ls to I0l5cc, and give a 97cc combustion chamber volume that would result in a 10.5:1 compression ratio in that application. When used with the Z2 crankshaft the result would be an 893cc engine with a 9.2:1 compression ratio, and a substantial improvement in performance compared to a standard 746cc Z-2. Si
