Yamaha RD 400


Make Model

Yamaha RD 400


1976 - 77


Two stroke, parallel twin cylinder, reed-valve torque induction


398 cc / 24.2 cu-in
Bore x Stroke 64 х 62 mm
Cooling System Air cooled
Compression Ratio 6.2:1
Lubrication Autolube


2x 28mm Mikuni carburetors


Battery, dual coils, breaker points   
Starting Kick

Max Power

44 hp / 32.3 kW @ 7500 rpm

Max Torque

41.1 Nm / 4.2 kgf-m @ 7000 rpm
Clutch Wet multiplate


6 Speed
Final Drive Chain

Front Suspension

Telescopic forks

Rear Suspension

Swing arm, dual shocks

Front Brakes

Single 267mm disc

Rear Brakes

Single 267mm disc

Front Tyre


Rear Tyre

Dimensions Length  1995 mm / 78.5 in
Width      760 mm / 3.0 in
Height   1060 mm / 41.7 in
Wheelbase 1320 mm / 51.9 in
Seat Height 800 mm / 31.4 in
Ground Clearance 150 mm / 5.9 in
Dry Weight 165.5 kg / 364.8 lbs

Wet Weight

171 kg / 376 lbs

Fuel Capacity 

16.5 Litres / 4.3 US gal

Consumption Average

43 mpg

Standing ¼ Mile  

14.1 sec / 90.1 mph 145 km/h

Top Speed

172 km/h / 106.8 mph

Source Cycle Guide of 1977

Dearly beloved, you can begin to wave good-bye to all those two-stroke roadsters we've known and loved for years. Kawasaki's KH400 triple has been laid away, and Suzuki has rung up the flower car for their two-stroke roadsters. The four-strokes have won the sales derby; more important, they have a better chance of winning the government emission tests. But before you get all teary and blow your nose, you should know that's all the bad news.

The good news is that RD400 Yamaha is still with us, and will be present or accounted for on the performance scene until at least 1980. And however attractive the old Kawasaki KH400 was, and how-ever utilitarian and -sturdy the GT-380 Suzuki was, there can be no doubt that the Yamaha RD two-strokes have been the most charismatic little rockets built in the last decade. So it has come to pass, as we climb the mountain of bureaucratic red-tape and finally see below us the Valley of the Shadow of Clean Air, that the first name in two-stroke performers shall be the last to go. Hallelujah: we can still do the reed-induction boogie.

If there's one word that describes the Yamaha RD400 series, the word is intense. The all-disc brakes are intensely powerful, an RD tradition since the motorcycles were disc/drum 350s. The RD Yamahas have always been quick steering motorcycles, thanks to a 52.5-inch wheelbase, 27.5 degrees of rake, 4.3 inches of trail, and a wet weight of 379 pounds. This kind of motorcycle isn't really guided into and manipulated through a corner; rather, RD Yamahas simply dart into the entry and out the exits.

If you weigh 185 pounds with riding gear, you're likely to dispense with a great deal of body English. Or if you must hang off, knee-out and whatever, then you do it with as much fluidity and precision as possible. An RD with a jerky, indecisive pilot on board becomes teetery and uncertain. Whatever you put into the bike, it tends to translate that input, amplify it, and feed it back to you. Call it intensity.

The engine has a high degree of sensitivity. The RD400 seemingly magnifies a quarter-inch turn at the twistgrip to a yards-long leap at the rear wheel. The engine is like the brakes: a little at the controls does a lot at the wheels. In about the first tenth-mile, the RD400E serves notice: be careful and well, or be foolish and sorry.

It's the way the two-stroke engine delivers its power that separates the RD400 from all the four-stroke twins. The four-stroke twins seem to accelerate by pulling themselves through the rev-range; though revs build with determination, no 400cc four-stroke twin goes through its rev-range with a blinding rush. By comparison, the RD400E delivers power in an explosive, instantaneous way. The revs build so rapidly that the tachometer always seems to be one shift behind.

If you rode the new Honda Hawk 400 four-stroke back-to-back with the Yamaha RD400E, you'd swear that Yamaha's two-stroke jet would yank the headlight right out of the Honda. The RD400E launches from a standing-start by lofting the front end, and a reckless clown could put himself into a vertical ground-loop. Moreover, a hard, fast shift into second can pull the front wheel right back up. When accelerating around cars the RD400E seems to cook along well, right to 6500 rpm, at which point the power rises to a real boil. On the other hand, the Honda Hawk, with an incredibly wide power band and no great blips in the power curve, is impressive only in the sense that it just drones forward: no eye-bulging, no breath-taking drama.

Imagine our astonishment when we discovered that the RD400E does the quarter-mile slower than the Honda Hawk. Our test RD returned 14.8 seconds at 87.71 mph in the quarter; the quickest Honda Hawk, as tested in the August, 1977 issue, clocked a 14.6-second/87.4-mph standing-start quarter-mile.

Confused and dismayed, we returned to the office, and checked the performance figures obtained by the RD4000, tested in the April, 1976 issue. That confirmed the fact that RDs can be fast; that particular test bike snapped through the quarter in a 14.15-second/94.36-mph pass. Furthermore, our sources at Yamaha International knew of no changes in specifications that would so radically diminish the performance between C-types and E-types.

The CB400 Honda makes more horsepower over a wider rpm-range than a RD400E. Over a 3500-rpm band, the Honda is putting out over 30 horsepower, peaking at 35.58. The RD400E dynoed over 30 bhp only in a 1500-rpm range, producing a maximum 34.18 horsepower at 7500 rpm. Furthermore, the RD400E jumped from 25.34 horsepower at 6000 rpm to 31.11 at 6500 rpm. That's what you call coming in with a bang.

On the torque side of the chart, you might expect that the Honda would show more pounds-feet over a broader spread than the RD400E, but this isn't quite how things turned out. The Honda stays over 20 pounds-feet through a 3000-rpm slot whereas the E-type is over 20 for a 2500-rpm band. But the Yamaha makes considerably more torque. The Honda peaks at 21.36 pounds-feet; the Yamaha pulls above 22 pounds-feet from 6000 to 7500 rpm. The 1976 RD400C — the 14.1 second bike—had a broader, fatter torque curve than the 400E Yamaha, to say nothing of the 400 Honda. All the evidence suggested that the 400E, in sharp tune, could run a much quicker quarter-mile.

Our tune-up included resetting the ignition timing to the specified 2.30 mm BTDC. The timing had slipped to 1.95 mm BTDC on the left cylinder, 1.99 mm on the right. We fitted NGK B-7ES spark plugs, a range hotter than the deposit-coated B8ES plugs that came out of the bike. The plugs were gapped on the narrow side of the spec (.020-inch to .030-inch) because the Yamaha ignition coils only induce the plugs to fire weak-looking whitish-blue sparks. Since the old 350 Yamahas were notorious for wispy sparks, Yamaha RD400-series bikes carry upgraded ignition coils, but we think Yamaha should still consider improving the upgrade. We'd like to see enough spark energy to power a small welder.

The tune up brought the performance up, but not much. The RD400E turned a 14.72/89.87 mph quarter—an improvement, but not the big one we expected. It was a 105 degrees at the dragstrip leaving the bike over-rich and the spark still seemed weak, but all excuses aside, the 14.7-second quarter disappointed us.

Few changes have been made in the RD400 since it appeared in the 1976 model year. At that time Yamaha re-engineered and re-worked the RD350 so substantially that the company in effect created a new motorcycle that only happened to look very much like the old one. (See Cycle, April 1976). After that, Yamaha did minimal updating. The RD400D had an altered paint scheme, a bit more fuel capacity, and a different seat. Again in 1978 very little has been changed.

The seat has been altered, this time sporting a crypto-road-racerish shell, very much like the one used on the XS400D last year. The cast alloy wheels have been painted black, and the polished aluminum edges of the spokes (and rims) highlight the wheels. The RD400D bore a Yamaha logo on the brake calipers; that script has vanished on the E-types. And with the new seat has come a new tail-light assembly, again identical to the XS400D unit. The E-type has a constant-on headlight, a safety "improvement" unknown on the D.

Most changes are cosmetic in nature, and it's not likely that Yamaha will alter the bike in any significant way in the near future. After all, since the departure of the Kawasaki KH-400 triple, and with the impending exit of the Suzuki GT380, the RD400E is the only 400cc two-stroke sports/touring bike available.

RD performance arrives at the rear wheel courtesy of an amazingly simple powerplant. In these days of 400cc four-stroke twins with one or two overhead camshafts, two or three valves-per-cylinder, and full complement of contra-rotating balancers, Yamaha's two-stroke twin seems like a monument to simplicity. The 64mm x 62mm (bore and stroke) cylinders draw air in through two 28mm Mikuni carburetors and two reed-valve assemblies. Reed valves have been used since the days of the old RD350 to spread out the power. Yamaha has succeeded in this respect, though the engine definitely begins to perk harder (as the dyno reveals) when the rev-counter needle swings past 6500 rpm.

The most interesting thing in the intake system is the RD400's anti-cackling, anti-surging modifications to the reed petals (uppers and lowers have different stiffnesses), the cylinders (.080-inch passageways in the cylinders lead from a point above the exhaust port windows, through the liner walls, and into the exhaust ports), and pistons (slots in the pistons' exhaust skirts open the crankcase to the exhaust port when the pistons are at TDC). The dynamics of this intake, crankcase and exhaust fiddling are complicated, but the result is pretty simple. It eliminates the surging associated with high-performance two-strokes running at partial throttle, say 45 mph in fifth gear, by weakening the out-of-synch resonating pulses that go through a two-stroke's intake and exhaust system just before the engine gets on its pipe, and all the pulsing comes into synch.

Pistons for these reed-valve twins have windows in the intake sides of the pistons. Slotted and windowed pistons are more likely to collapse with prolonged use and get rattly. Moreover, much of the area in a reed-valve cylinder is taken up by ports, so that the liners offer less contact area for the pistons than might otherwise be the case. The ports-everywhere liners and shrinking pistons eventually produce enough racket to be noticed. This two-stroke clatter is nothing too serious, just annoying and normal.

Yamaha went to a great deal of trouble to silence the RD400 series; indeed, on the induction side, a mammoth air-box filter-unit was designed to hold down the noise and still pass a sufficient volume of air to maintain the aspiration-requirements of the engine. The sheer size of the airbox necessitated a redesign of the frame behind the engine and below the saddle. Despite Yamaha's efforts, the RD400E is still a noisy machine at start-up and idle. There's a fair amount of intake honk that is supplemented by piston/ cylinder noise and well-defined pop-pops from the exhaust pipes. But if you like two-strokes, it's not a bad cacophony at all.

Two-stroke twins have a vibration problem that's not as severe as the 400cc four-stroke twins. Or at least the two-stroke's problems make solutions easier. The low-amplitude, high-frequency vibrations in the RD400 are mainly isolated by rubber-mounting the engine. This allows the engine to vibrate furiously on its soft mounts, but the vibration stays away from the rider. In an effort to be thorough, Yamaha has rubber-mounted the footpeg holders, so only by touching the engine is the rider aware of the unit's activity. Rubber joints between the head pipes (that bolt directly to the shaky engine) and the mufflers—solidly attached to the frame—flex enough to keep the exhaust system intact.

The new saddle is lower and firmer than the sitzer fitted to the original RD400. The first 400 always gave the rider a sensation of sitting on top of the machine, and having to reach down to find the motorcycle. The RD400E, by contrast, positions the rider so that he feels more part of the motorcycle, more in it. One-hundred and fifty miles is an easy distance to ride the RD400E. As the miles roll by, the motorcycle becomes less comfortable though that's not really a function of the saddle. The small physical size of the RD400E cramps larger riders over long hauls.

Staffers warmly remember the freeway manners of the first RD400 which had an almost BMW-type ride. The E-type feels as if it's sprung more stiffly than the whoosha-whoosha RD400C. Other current-year Yamaha street bikes have stiffer suspensions than before, in part a recognition that super-soft springs cause the motorcycle to nose-dive under braking and to lose cornering clearance, and in part a response to riders who accessorize their bikes with heavy fairings and other touring gear.

In the suspension department, our main complaint centers on the rebound damping of the shock absorbers. The damping gets limp after you've been thrashing around on bumpy back-country roads, and that causes the RD400 to feel vague and rubbery in a corner. Riding the Yamaha really quickly is a task that takes a lot of concentration, and it's the kind of bike that you like to get through a corner in one swoop with no corrections at mid-passage. It does nothing for your concentration or tidiness to discover that the RD is beginning to waggle.

There are other reasons to keep your focus while jetting with the RD400E. The disc brakes work with an almost ferocious effectiveness; unless you exercise a certain amount of care, you could overbrake and lose the bike. Applied somewhere near their limit, the brakes will let you plunge so deep into a corner that you stop breathing from entrance to apex. Hopping on the gas too hard in a first- or second-(and sometimes third-) gear corner can get the front end very light, and you must recognize that a hot throttle hand can unload the front end enough to make steering highly problematical. The Yokohama Speed Master tires stick very well under acceleration, braking, and cornering loads; nevertheless, given the forcefulness with which the RD400E can be ridden, a rider must make sure he doesn't pass through the tires' margins of safety.

On a freeway, the RD400E has enough suspension compliance to iron out most of the small ripples and breaks in the pavement. However, the effect of hitting joint seams between the concrete slabs can be felt at the handlebars. For steady-state freeway cruising we remember the softer-sprung RD4000 as more comfortable on the great concrete roadways. While the riding position, saddle comfort, and vibration control make RD400E an acceptable go-to-work and errand-running motorcycle, that seems such a waste. Though one staffer has an easy seven-mile home-to-office commute (comprised of two miles of boulevard riding and five miles of freeway), he found himself running the back-route to the office through 12 miles of twisty roads.

To be sure, the RD400E can toot down the freeway, offering most all those convenience features typical of Japanese motorcycles, including the trick Yamaha directional signal that measures distance and shut itself off automatically. Still, if you're the kind of guy who eyes the freeway exits looking for an interesting road to add to your collection, then you'll intuitively understand the RD400E. And you'll rejoice in the Good News that this high-performance two-stroke is still alive and well in 1978

Source Cycle Guide


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



• 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 drive-train 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.


• 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.


• 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 tri­ple-point 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.


• 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 top-end 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 re-vamped 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