Service
SERVICE
DEPARTMENTS
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.
CBX SUSPENSION
I own a 1979 Honda CBX. After reading about the changes made to the 1980’s suspension, I would like to know if these can be adapted to the ’79’s. Such as swing arm bearings, shocks, and air caps on the forks. Also, at low rpm (900—1000) I’m getting a rattling down by the clutch, which quits when the lever is pulled in or when it’s engaged. I’ve been told this is common on plain bearing cranks, but my brother’s XS11 doesn’t suffer from this.
Rick Hegerfeld Lodi, Wis.
Swing arm bushings on the '80 CBX are not interchangeable with those on the '79. The combination needle and ball bearings on the ’80 use a larger diameter swing arm shaft (16 vs. 14mm) and a larger bearing O.D. at the frame. The new 1980 Euro-style shocks, however, will bolt right on to your '79. If the plastic swing arm bushings wear out and give you trouble, you might consider replacing them with a set of bronze bushings, available through Ontario Moto Tech Corp, 6850 Vineland Ave, #18, North Hollywood, Calif 91605.
Honda tells us the new variable-rate fork springs will probably fit into the '79 stanchion tubes, as will the air caps. They've done no testing on the advantages/disadvantages of that combination, however, and stress that a switch to the '80s shocks and the new V-rated tires will yield the most immediate and gratifying handling improvement.
The rattle you describe is probably friction disc and plate vibration in the clutch basket. Nothing to worry about, and you can often reduce the clatter with a careful curb synch and a smoother idle.
SUPERTRAPP
What exactly are “Supertrapps”? I’ve read a comment here and a comment there about them, but can’t recall ever seeing them advertised. My Sportster looks classy with its drag pipes, but I never realized how obnoxiously loud it was until I moved from the city to the quiet lake community where I presently reside. Incidentally, there’s a guy out here who runs ’em on his boat. He says it came with them and he doesn’t know any more than I do. How ’bout that?
S. McNulty Hamburg, Mich.
The Supertrapp is an aftermarket muffer designed to reduce noise on two and fourstroke off-road bikes without creating excessive backpressure. It offers an adjustable feature wherein any of 12 “diffuser discs” may be added to or subtracted from the end of the muffler core, allow ing the owner to dial in whatever level of noise and/or backpressure suits his purposes. Adding discs— oddly enough—increases the noise level; removing them quiets it down. It also provides Forest Service-approved spark arresting capabilities. The muffler body and core kit are sold separately, so that either a twoor fourstroke core can be fitted to the same body.
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Discojet, the manufacturer, doesn’t advertise the Supertrapp as a street-legal mujfler because it doesn’t meet minimum Federal noise requirements, but it would be a whole lot quieter than the drag pipes, and probably less raucous than most of the aftermarket megaphones, shorties, etc. available for the Sportster. They come in a range of 20 tailpipe O.D. ’s, from 0.75 in. up to 2 in., so there would be no problem fitting one to a Sportster pipe. The muffler body costs $11.95 in black and $22.95 in chrome; the four-stroke core kit is $22.95. And for more silent running, an add-on resonator is available for another $5.95. You can order the Supertrapp through any dealer who carries Helmet House, Wheelsport, or Rocky Cycle catalogs. Or contact Discojet, 920 3rd St., Davis, Calif. 95616.
XS JETS
I am planning on buying the 1980 Yamaha XS11 Special and I would like some information. I have read that the ’80 XS11 has been leaned out and the jetting fixed to prevent tampering. I would like to know what the procedures are for rejetting and also if anything else would have to be changed after rejetting it.
Tim Cade Bremerton, Wash.
Our advice—and Yamaha’s—is that you put some miles on the XS and see how you like it before making any substantial changes. In stock form the Eleven suffers from no real dearth of power, and with 1980 cam and ignition timing the bike may run best with standard jetting. If you have problems with excessive leanness, Yamaha dealers have a kit (available only with factory exhaust gas analyser) that allows them to adjust for optimum timing and idle mixture within Federal specs.
The ’80 XSll is indeed leaner than its predecessors, with #115 main jets on cylinders 1 and4, and # J20’s on 2 and3. Earlier models used a #137.5 straight across. The jets on the ’80 XS remain interchangeable, but the needles have lost two of their three adjustment slots and are now set in a permanent lean position. Earlier needles and clips, however, will fit right into the new curbs. Switching needles and jets is easiest if you remove the carbs and do your work on a well-lighted bench rather than trying to remove the float bowls in place. No other changes in tuning should be necessary to accommodate a minor jetting adjustment. A It is illegal, of course, for any dealer or professional mechanic to modify the jetting on your bike, but in some states the owner is still allowed to make his own changes. Best to check on your state and local laws. Again, we recommend you try the bike as is. Then if you want to go a bit richer the E-serie4 needles and jets—or something between the # 120’s and # 137.5’s—might be worth a try. 1
SPEEDO BACKDATE
I recently read in the July, 1979, issue of your magazine about a new government regulation that limits the maximum read* out of a motorcycle’s speedometer to 85 mph (effective for all cycles built after September 1, 1979). My questions are these: ^
1. How are they going to get a speedo, that has a readout of, say, 160 mph maximum, down to 85? Does this involve re* gearing the speedo or adjusting the cable?
2. Could someone, if he wanted to,readjust an 85 mph—or any other speedo, for that matter—to read the inner kilome-^1 ters per hour as miles per hour?
3. I would like to know how one would adjust a speedometer that is reading 6Ç} mph when the vehicle is actually doing 55, or vice versa, and also, how do you adjust a speedo that’s correct only part of the time so that it is correct all of the time? (Reading* one speed correctly, but another incorrectly is an example.)
John R. Morgan ' Northfield, Mass.
Speedometer gearing at the wheel otj most 1980 motorcycles remains unchanged from last year, so the cables are turning aL ’79 speeds. The changes have all been made at the speedometer head. General practice* has the cable driving a disc-shaped magnet which spins within—but does not touch—a bell-shaped steel hood. This hood is mounted on a shaft with the speedometer needle. Cable (and magnet) speed consequently translate into degrees of needle movement on the speedometer face. The,, ratio of degrees of movement to cable rpm is governed by the strength of the return spring on the needle. So what we have on the new generation of 1980 See-No-Evil speedometers are weaker return springs and pathetic, double-digit numbers painted farther apart on the dial face. ^
Which is to say that you’re going to have a pretty hard time changing, adjusting, or otherwise improving the sealed, pre-set unit on your bike. The easiest—and most expert< sive—fix is to replace your speedo with a ’79 head. Most ’80 models, provided they were'* produced in ’79, are set up for a direct retrofit (but call your friendly parts person to make sure). The replacements are not ' cheap. A ’79 speedo for any of the mediumto-heavyweight road bikes will cost any* where from $75 to $115. A ’79 Honda 750F speedometer, for instance, will slide across the counter for a cool $106.40.
The cheapest alternative, of course, is to live with the 1980 dial and tell yourself that the road at 85-plus is always more interesting than instruments. That, or calculate your top-gear mph off the tach. It is some *consolation that the current crop of speedometers offers greatly improved accuracy over many of the old ton-up types which were, in some cases, off by as much as 20 percent.
GREASED HONDA
> I am the owner of a 1978 Honda CX500. The official Honda service publications state with reference to the lubrication of the driveshaft joint (through the grease fitting on the rear drive housing) that this joint be lubricated every 7500 miles with 1.5 ounce (45cc) of lithium based multi-
-purpose grease. Let us say that after 22,500 miles or three recommended lubrications of this driveshaft joint there will be 6.0 ounces of grease, including the grease from the factory if there was any in there. Where does the old grease go? Does the final drive need to be taken apart periodically and ».cleaned out?
Adam Schoolsky Beverly Hills, Calif. The only problem here is that the shop
* manual isn't as detailed as it should be.
You don 7 have to clean out the old grease, nor need you dismantle the shaft housing.
When you pump the fresh grease in, it moves the old grease out of the way. A nd because ythe housing is all but hollow, there's space for several thousand services before it's full, By that time, say a few million miles, chances are you 'll need to rebuild the driver train anyway.
LOW YAMAHA
^ I’m a-short redhead who’s getting gray roots. I own a ’79 Yamaha 650 Special 2F and 1 need to lower the bike. Lowers for 650 Yamahas only go to ’76. I tried them
and they are too short. I inquired of many different mechanics who told me I can’t use another shock and can’t use a different .coil. Why? I don’t want a little bitty tire back there cause the one I’ve got looks
good—nice and fat like it is. I have a custom seat on now so that’s out. Is there
anything specific you can tell me other than machining my own lowers?
Kathy Seibrecht Milwaukee, Wise. v There's no reason why you couldn't use shorter shocks on your Yamaha 650. You would however have to also use a stiffer spring because the shorter shock would have less travel. If you had the same spring rate as original with less travel, the shocks would bottom out.
* Many manufacturers offer replacement shocks for the 650 Twin. Normally these have a 13 in. fully extended length with about 4 in. stroke. You could replace these with 11 in. shocks having a stroke of about 3 ' in. For example, in the S& W range use a D-7 shock with a 100 lb./in. S-8 spring to achieve this. The rear end would then be powered by about 1. 7 in.
In this instance it’s worth taking your bike along to a dealer at the same time to find if there is enough clearance around the f rear wheel to do this modification. You might otherwise cause the tire or drive chain to touch the chassis, which is potentially
dangerous.
>
URAL PARTS
I have a Cossack Ural and I am in need - of wheel bearings and other parts. Please help if you can.
Edward Beaudry ^ 1035 Candía Rd
Manchester, N.H. Check with Sidecar Restorations, 115 S. 20th, St. Louis, Mo. If anybody has it, they rwill.
SUZUKI TORQUER
*■ With an engine such as the Suzuki GS1000 has, is it possible to increase the mid-range torque without a big-bore or stroker kit? Are the camshafts already Aground for optimum mid-range torque? Or would a regrind be beneficial?
I suppose I am seeking the ultimate touring bike; a bike with the looks and the power of an XS Eleven Yamaha and the handling of a GS1000. Maybe a GS1000G with engine mods.
Richard Lopez Roy, Utah.
r While the Suzuki GSIOOO’s double overhead camshaft engine gives excellent performance, the factory wisely tuned the cam Riming and lift to also give good mid-range power.
It is doubtful you could make a significant improvement in the mid-range torque + without sacrificing power elsewhere in the rev range simply by changing the cam timing. An increase in the compression ratio y ould certainly boost power all through the range, but you would have to run the engine . on higher octane fuel, which could be hard to find, to prevent detonation.
* Although it involves a complete engine strip-down, the best way to improve midrange power and torque is by boring the cylinders andfitting bigger pistons. Without *any other change you can expect a fattening of the low end and mid-range.
R.C. Engineering (13300 Estrella Ave., v Los Angeles, Calif. 90248) offers an 1176cc big-bore kit that would be perfect for your needs. It uses 76mm pistons and involves the fitting of larger liners. A t the same time we ’d *¿1Iso recommend the welding up of the crankshaft to prevent twisting.
