Yamaha TX500
Years produced: 1973-1978
Claimed power: 48hp @ 8,500rpm (claimed)
Top speed: 98mph (period test)
Engine type: 498cc air-cooled DOHC 8-valve parallel twin
Transmission: 5-speed
Weight: 456lbs (wet)
MPG: 40-55
Price then/now: $1,395 (1973)/$1,000-$2,500
In 1973, the motorcycle market hadn’t yet gone cubic inch crazy, and 500cc was still considered a generous size for a street bike. At the time, the lion’s share of motorcycles in the half-liter class were 2-strokes. While Yamaha had enjoyed considerable success with its RD250s and 350s, it needed a new machine to place between these and the TX650 twin (as the 650 had just been renamed), and their new flagship counter-balanced TX750 twin. The resulting Yamaha TX500 was Yamaha’s first foray into midsize 4-stroke territory, and while initial impressions were highly favorable, the TX500 proved less than easy to live with, perhaps because it was a little too high-tech for its time.
On paper it looked promising and bristled with innovation. The 180-degree, short-stroke parallel twin boasted dual overhead camshafts and four valves per cylinder for high-revving, class-leading power. Following in the footsteps of its big brother, the TX750, the TX500 twin used Yamaha’s “Omni-phase” balance shaft to quell the inevitable parallel twin buzzing. Mated to a 5-speed transmission with electric start and equipped with a front disc brake, this thoroughly modern engine made Triumph’s pushrod, 4-speed, kick start, drum-braked Daytona 500 look positively archaic.
TX500 styling was modern, too, with smoothly integrated engine castings, one-piece dash, sleek gas tank, upswept mufflers and plenty of chrome. The TX500 was comprehensively equipped, with an up-to-date electrical system well able to cope with the electric starter. Testers liked that a single key worked the ignition, steering lock, seat lock and gas filler cap. Yet with all its seeming improvements, the TX was a leap into uncharted territory.
Period test reports, while noting a relative lack of torque at low to mid revs, noted “a good blast of power” from the revvy engine and praised the bike’s slick-shifting transmission. The TX’s handling inspired confidence too; good ground clearance and overall balance made it easy to maintain a chosen line. However, testers found that cornering above 70mph could induce mild steering wobble, which while never dangerous could be a little disconcerting. Brakes, borrowed from the RD350, worked perfectly well, though the front disc required a firm pull and the rear was perhaps a little too powerful.
Unfortunately, things went slightly awry with power delivery. First, the engine was noticeably cold-blooded and needed a good warm up before it would run without the choke. And even when warm, at least one tester experienced problems with the engine sometimes dying when the throttle was backed off — not closed, just reduced. Other riders reported that if the engine was allowed to idle for a few seconds (at a traffic signal, for example), it had a bad habit of stalling when the throttle was cracked open. Testers also noted surging at small throttle openings, and blamed the Keihin CV carbs, noting that Honda had experienced similar issues with the same type on the CB450.
These problems likely could have been overcome with some tuning, but the twin’s 180-540 degree firing interval and relatively light flywheel also meant that below 3,000rpm, power delivery felt rough and uneven, turning into, in Cycle Guide’s experience, “violent lurching” if the rider allowed their speed to drop below 10mph. That meant riding in traffic was a chore, requiring a lot of clutch slipping and careful throttle control. This wasn’t helped by slack in the push-pull throttle cable mechanism and lash in the transmission, much of it down to the cush drive springs in the clutch. Compounding this, the TX500 was geared relatively tall, yet produced its best power only above 5,000rpm.
There were maintenance issues, too. Spark plugs were hard to access, and while the valve clearances were easy to adjust, both the cam chain and the balance shaft chain required manual adjustment. And the adjusters were buried deep in the engine: The alternator had to be removed to adjust the balance shaft chain at the prescribed 6,000 mile interval.
Perhaps the TX500’s biggest challenge to success came from within its own camp. The RD350 (as well as the later RD400 and RZ350) produced at least as much power and cost less. The simple two-stroke engines were smoother and more responsive, and lacked the herky-jerky power delivery of the DOHC twin.
The TX500 became the XS500 in 1975, following Yamaha’s decision to drop the disastrous TX750 twin, and 1976 brought a makeover with the XS500C, with improved carburetion, heavier flywheels and less tranny lash. Automatic cam chain adjustment was introduced on late C models, a decided improvement over the previous setup. Styling was revamped with alloy wheels, a rear disc brake replaced the drum, and the front end received new Showa forks.
The 1978 XS500E marked the end of the line, yet almost predictably it was the best of the bunch, as by this time Yamaha had purged the little twin of just about all its vices, turning it into the fine little half-liter bike it always wanted to be.
Although Yamaha had finally gotten it right, the world had changed. The performance race was on, and sporting riders could choose from a wide range of 750-900cc multis. The half-liter class was no longer fertile ground for Yamaha, so Yamaha axed the 500 from its lineup. Interestingly, at the same time Yamaha dropped the 500, Honda, Kawasaki and Suzuki all introduced 400cc 4-stroke twins that owed much of their technology to Yamaha’s pioneering TX.
Half-liter rivals to the Yamaha TX500
Suzuki T500 Titan/GT500
• 47hp @ 7,000rpm
• 492cc air-cooled piston-ported 2-stroke parallel twin
• 5-speed
• TLS drum brake front (disc front 1976)/SLS drum rear
• 408lb (dry)
• 30-40mpg
• Price now: $1,400-$3,000
Like the TX500, the Suzuki T500 was also hailed as revolutionary on its introduction in 1968. Conventional wisdom said you couldn’t build an air-cooled 2-stroke twin of over 350cc because it would be prone to overheating and seizing, but Suzuki did just that, and also created the largest capacity Japanese bike on the market.
Early T500s earned a reputation for excessive fuel consumption, pernicious vibration and unstable handling, issues mostly addressed with the MkIII in 1970. Other niggles: a transmission that wouldn’t shift into first from second while moving (an intentional “safety” feature), and tachometer drive off the countershaft — the tach didn’t read if the clutch was disengaged.
By 1974, with the speed stakes firmly in the grasp of the new Superbike generation, the T500 was marketed as a mild-mannered tourer at a very competitive price point, its anachronistic drum front brake underlining the economy theme.
A disc brake and a new designation, GT500, came in 1976, its last year.
Triumph T100R
• 41hp @ 7,200rpm (claimed)
• 490cc air-cooled OHV parallel twin
• 4-speed
• TLS drum brake front/SLS drum rear
• 396lbs (wet)
• 45-60mpg
• Price now: $4,000-$10,000
As the granddaddy of half-liter bikes, the Triumph T100R Daytona was pretty stale by 1973. But it still had the giddy-up to give the TX500 a run for its money. Cycle magazine’s dyno recorded 36hp for the T100R and 37hp for the 1973 TX, but the Triumph was 60lbs lighter. Even so, the TX’s broader powerband and five speeds made it faster in the standing quarter at 13.7 seconds versus the T100’s 14.7-second time. On the street, however, Cycle’s test rider said he could only outpace the Triumph if he used the last 10 percent of the Yamaha’s performance.
The two-valve OHV formula was tried and tested, and its rugged simplicity still makes it attractive. All you needed to strip the engine was a basic tool kit and a pinion puller. Ease of maintenance apart, Cycle concluded the only thing the T100R excelled at was “being a Triumph.”
Time had caught up with the T100. Kick starters and drum brakes were now dirt bike territory. In November 1972, Triumph introduced the single-carb, BSA-framed TR5T Trophy Trail, the final development of the T100 line.
