Yamaha XS 500

Although looking like the smaller XS400 and XS250 bikes, the XS500 has a different twin-cylinder engine which features twin-overhead camshafts and four-valves per cylinder.

Although such an engine would be ideally suited to a sports motor cycle, Yamaha instead have used it in a state of tune for a bike they classify as a tourer with enough engine power to enable it to keep up with larger capacity machines.

The oversquare power unit displaces 498CC and with a compression ratio of 9.6:1 produces 49bhp at 8500rpm, just one brake horsepower down on the company's 650CC twin.

A four-valve-per-cylinder engine is used because four small valves use space more efficiently than two larger valves, so that, in fact, more head area can be utilised which in turn makes the engine more efficient. Also the lower reciprocating mass of small valves, means higher engine speed before 'bounce' is induced, and better ignition is helped by the sparking plug being central in the head, its most efficient position. The problem with the layout is that to get the valves in an efficient semi-hemispherical head, twin overhead camshafts have to be employed or a complicated system of pushrods and rockers which would negate the effect of the extra engine speed gained from the layout. The XS uses direct-operating overhead cams which make servicing more complicated and time consuming.

The Yamaha has pistons set at 1800 unlike many four-strokes with their 3600 layout with the inherent vibration difficulties. However, Yamaha had the problem of the crankshaft rocking with the alternate reciprocation, so to encounter this they use their patented 'omniphase' balance shaft.

The top speed of this 425lb bike is 105mph, while it will accelerate over a quarter mile from standing start in 14.3secs; fuel consumption is 46mpg. In all, the XS500 is deceptive for it is more advanced than it looks and 'four-stroke twin' specification suggest.

THE SPORTING MIDDLEWEIGHTS

Honda CB550F, CB500T, Suzuki GT380, GT550, Yamaha RD400C, XS500C, and Kawasaki KH400

Triple comparison

Other than the predictable responses that always follow the publication of a Cycle Magazine street-bike comparison test ("You guys are full of it!"), the most persistent—and plaintive—comment is, "Do one on the Middleweights." So here one is—a Middleweight Comparison Test, including two entries from Honda (CB550F and CB500T), two from Suzuki (GT380 and GT550), two from Yamaha (RD400C and XS500C) and one from Kawasaki (KH400 Triple). The bikes we've selected for this comparison may or may not jibe with your idea of what constitutes a proper Middleweight, but we feel that the selection process was valid and re­sponsible. To fanciers of the Honda CJ360T, Honda CB360T, Kawasaki KZ400 and Yamaha XS360C, we say, too small, too econo-oriented. To those loyal to the Hercules Wankel 2000, the Benelli 500 Quattro and the Laverda 500 Twin, we say, too exotic.

At the center of our Comparison Test was a 1300-mile toot from our Westlake Village offices out across the desert, then Northwest following the Sierra mountains to San Jose, then down along the Pacific Ocean and home. The trip lasted for five days, during which time each of our test­ers rode each bike five separate times, and had a chance to sample every bike in every kind of terrain. At the end of the ride, the testers were asked to fill out score-sheets.

Categories in which the bikes were evaluated were Overall Engine Performance, Overall Comfort, Fit and Feel, Overall Noise Level, Vibration Control, Suspension Compliance, Mountain Road Handling and In-Town Ease of Operation. Possible scores ranged from zero—unac­ceptable—to nine—outstanding. The final results in each category were determined by averaging the scores of all the testers; the overall rank order was determined by the category scores and by the staff's subjective opinions.

Accompanying those members of the staff still able to get around after the Great Dirt Donk Expedition were three outside experts: Bob Johnston, who had been with us on the Donk trip and the "Eight for the Open Road" comparison (August, 1975); Marty Dickerson, Bonneville record holder and motorcycle mechanics instructor at the West Valley Occupational Center in Woodland Hills, California; and Bill Ocheltree, former Motorcyclist Maga­zine staffer and currently a freelancer. They were invited hopefully to offset the hell-raising tendencies of the staff; as it turned out they raised more hell than we did, even though all three of them are between 40 and 50 years old

Capsule Summaries

HONDA CB500T

One-time progress is a one-time thing; if ever a mechanism bore testimony to that idea, it's the Honda CB500T. The bike came to these shores in the mid-Sixties as the second largest-displacement Jap­anese motorcycle (the 650cc Kawasaki was first) of all time, and was trick beyond belief. It was a vertical parallel twin four-stroke with double overhead cams, tor­sion-bar valve springs and the most com­plex cylinder head casting anybody had ever seen on a motorcycle. It was ugly; Honda fixed that in short order, and by the early Seventies the 450 was generally held to be superior in all regards: it was fast, handled well, was easy on maintenance, had a disc front brake and was a marvel of smoothness when matched against other bikes of the same general description (the Triumph 500 and 650 among others).

Had Honda clung to the 450 as we knew it then and simply dragged it forward year after year with no significant changes, chances are that, in the face of giant strides made by Honda's now plentiful competitors, the bike would not have fared well. But it would have done better than the current 500T, because the old 450 was a better motorcycle.

The 500 is a cosmetic masterpiece; the T-bike is lovingly painted, plated, styled, trimmed and striped Its appearance is its message; once you plunk your buns on the saddle and fire up the engine, it's all downhill. The center console vibrates it­self into a blur; the footpegs and stands all stick out too far; the bike leaps ahead and falls back with a will of its own; the brakes on both ends need to be improved; the rubber-mounted handlebar does little to shield your arms and hands from the engine's incessant quaking and shaking.

Well, you're thinking, it's probably cheap. Wrong-o. It costs $1610, suggested retail, or $400 more than the RD-400C or the Kawasaki KH400. Well, maybe it's fast. Guess again. Does it get good mileage? Yes—just under 40 mpg over the duration of our comparison.

Only under the most carefully chosen set of circumstances could the 500T be presented as an admirable motorcycle; it does look good, probably won't break, and will be economical to operate and not especially fussy. But in this displacement range, you can do so much better—as our comparison will clearly show.
A stunning blonde appeared on Cycle's June 1971 cover along with the first CB500 Four, and a bold description which read "The Honda Magic Lantern Lights Again." After electrifying the industry in 1969 with a 750 Four, Honda was back at it two years later, injecting a massive dose of technical class and good motorcycling into a rather ordinary collection of mid­sized street bikes. The miniaturized 750 offered smaller people with smaller budgets the same prestige, technology, reliability, comfort and grand-prix exhaust note that the heavier, more expensive 750 had used to unseat the reigning kings of motorcycling. Reduced size gave the 500 an important advantage over bigger bikes—agility, nimbleness and better handling—and a strong appeal for those who could appreciate subleties.

The little Four was a brilliant motorcycle and a big seller. Within two years Honda updated it to performance levels reached by other brands reacting to the original CB500, and thus the 550 was born in late 1973. The extra 50cc brought the displacement up to Suzuki's 550, helped justify a price hike from $1500 to $1600 and ensured that several other costly improvements would not go unnoticed. For 1975's model year the CB550 four-piper was joined by the bike in this test—a sportier-styled CB550F which featured a four-into-one exhaust, a new tank, center key location, different seat and the im­plication that Café styling and even higher pricing might be accompanied by more engine performance. It wasn't. The bike still has more horsepower than any other in the test, and engine performance equal to everything but the RD400C's acceleration and the GT-550's top speed.

As a five-year-old basic design, the 550 is mature by Honda standards, and that means there aren't any detail problems left. Its tiny features have come to be expected from the Japanese, and they're there in droves on the 550F. The bike's maturity also means you're stuck with its shortcomings, which are drivetrain snatch and dragging chassis hardware in fast right-hand corners. The gearbox, still clunky and uncertain after five years, is another item you'll have to put up with.

Nothing else about the bike requires tolerance. Mostly the CB550F is delightful, but it comes at a price ($1825)—the high­est in the group by 8 percent. Neverthe­less it will still sell more units than any of the others because more dealers have it, because it's a four-stroke, and simply because it's a Honda.

KAWASAKI KH400

The KH400 is the best of all Kawasaki three-cylinder two-strokes. To appreciate that, you have to understand where Ka­wasaki was coming from in 1968, and where they're coming from now. In the late Sixties it became evident that Ka­wasaki, which had always seen itself as a performance company, was prepared to take no prisoners in the drag-o-derby. The H-1 500 was a menacing little monster: quick, unstable, unpredictable and terrifyingly fast. The 750cc version debuted late in 1971, and was even better—or worse—than the 500 because it was faster. But the 350cc triple, presented in early 1972, was somewhat tame. It was quick and quirky, in that fine Kawasaki tradition, but it showed the first signs of the company's willingness, having become "established," to view restraint as a not altogether unacceptable quality. Shortly thereafter Kawasaki introduced the Z-1— that factory's first, quality, non-disposable motorcycle—and their bikes have been getting more attractive ever since. The bike in question here, the KH400, is significantly different from its predecessor and continues Kawasaki's quest for more-decent and less-flashy equipment.

It has been freshened-up in many areas for 1976. Its air inlet system is new, its chassis is more liberally gusseted, its muffler has been re-engineered for better sound control, gearing has been stretched to help mileage and reduce cruising engine speed, and the KH has been fitted with a CDI ignition system to prolong plug life.

But even with its little package of developments and refinements, the KH re­tains the kind of character that had it highly-placed in several of the performance-intensive test categories, and ranked down near to the bottom in the categories that emphasized comfort. It's light (the lightest in the test at 378 pounds with a full tank), inexpensive ($1239 suggested retail) and has the kind of power-to-weight ratio (12 Ibs/hp) that guarantees invigorating acceleration. It is also, in keeping with the larger displacement Kawatriples that preceded it, a bit harsh in terms of finish, styling and myriad details which other factories handle more delicately. But crude or no, the KH is a genuinely fun motorcycle to be around— as long as you're tuned into good han­dling and hot engines.

SUZUKI GT380

The Suzuki GT380 Sebring was the first sub-400cc street bike to break away from the 350cc class rating. It was also the first mid-displacement multi-cylinder roadster from Suzuki. In the wake of the performance bikes of the early Seventies, the Sebring navigated in a very different direc­tion, and moved toward serene perfor­mance and exceptional comfort.

In designing the GT380, Suzuki's engineers mixed fresh concepts with proven parts. The bore and stroke of the Sebring are the same as Suzuki's 250cc street twin. By adding one cylinder the displace­ment was bumped up to 371 cc. Mild port timing, low compression and small carburetors level out the 380's power and separate it from pipey, performance-type two-stroke engines.

The six-speed gearbox is also of the same design as the GT250 twin's. Gear spans are progressively tightened up in the higher cogs and there's nothing un­usual about that, but it does allow a rider to find a gear in which the GT380 is absolutely smooth on the highway.

For all intents and purposes the engine has remained unchanged since its release in 1972. The Ram Air System has proved efficient in increasing engine heat dissipa­tion, and more importantly, reducing operating noise. The low compression motor runs trouble-free on regular grade gasolines. Suzuki's intricate oil injection system lubricates the pistons and crankshaft bearings individually and includes a re­cycling arrangement which removes fuel mixture accumulation from the crankcase areas and feeds it directly into the com­bustion chambers.

In 1974 a number of major changes were made to the chassis, carburetor intake, exhaust and instrumentation. The chassis was completely redesigned to improve handling and Ground Clearance. Better fork internals, shock dampers and springs delivered a better ride. New instruments were joined by the digital gear read­out and larger warning lights.

Bell-crank operated carburetors replaced the cable-actuated mixers and the mufflers were moved up and in for addi­tional Ground Clearance. Modifications to the intake system reduced objectionable in­duction drone and relocated footpegs and controls increased comfort.

Suzuki built the Sebring with a front drum brake only in its first year, moving to a disc in 1973. Rubber engine mounting is unchanged, having proven effective in eliminating vibration. The conventional triplepoint ignition system is driven from an independent idler gear to prevent timing fluctuation associated with crankshaft flexing.

Initial saddle and gas tank designs have gone without alterations. Minor design improvement changes have been made to the GT380's through its five model series, but few are visible. Suzuki believes in improving the breed from the inside out, not the outside in. The GT380 has successfully survived four tough years, and Suzuki appears willing to retain the Sebring indefinitely.

SUZUKI GT550

There is little new and nothing unconventional about the '76 Suzuki GT550 Indy. It is a four-year old motorcycle that was designed to ride the waves of progress, survive as a seasoned veteran and never get out of date. Paint scheme alone identifies the 1976 Indy as new.

Suzuki's innovative design of the Ram Air cylinder head shroud system has endured, unchanged, since the beginning. Ahead of its time in 1972, the RAS provides dual benefits. The scoop increases air-flow activity over the fins, and also functions as an excellent sound-deadener to minimize the amount of topend piston noise.

There have been no performance changes made to the cylinders or pistons since the Indy's inception. The low-com­pression two-stroke triple was designed for durability and runs as happily on low-or no-lead fuels as it does on premium. Unchanged since the GT550's original design is its exceptionally effective rubber mounting system.

Only one chassis change has been made to the GT550 through the five-model series. In 1974 a number of major up-dates were built into the Indy—mostly to subdue noise and improve handling. The carburetion, intake and exhaust systems were modified to reduce operating noise levels. The exhaust pipes were tucked up closer to the frame, the side stand and center stand were moved in and the foot pegs relocated to give the Suzuki additional lean angle clearance. The frame changes amounted to nothing more than relocating foot controls and brackets to which they attached.

New instruments were fitted to the Indy in 1974 and included Suzuki's popular digital gear read-out and bigger idiot lights. The five-speed gearbox is identical to the transmission in the big 750cc Suzuki LeMans. The 550's clutch and primary drive are equally robust.

Suzuki went to the disc front binder in 1973. The rear drum brake and wheel have remained unchanged, as have the tire sizes.

Electric starting was in the first 550, and has remained without alteration. Most of the electrical components are the same as those used in the 750s. The plush saddle and four gallon gas tank have been changed in very minor ways—a new piece of vinyl here and a fresh paint stripe there. Minute internal modifications appear in the parts books of each new Indy, but the motorcycle remains pleasantly the same. Unlike most revamped new models the GT550 has lost seven pounds since 1974 and the price has escalated only moder­ately. As Suzuki's most successful road bike, the GT550's reputation for depend­ability is a matter of record.

Source Cycle World