Tomorrow’s Classics: 1973-1977 Suzuki GT250, a 247cc parallel twin 2-stroke.
Suzuki GT 250
Claimed power: 31hp @ 7,500rpm (see text)
Top speed: 91mph (period test)
Engine: 247cc air-cooled piston-port 2-stroke parallel twin
Weight: 320lb (dry)
Price then/now: $810 (1973)/$1,500-$2,500
By the 1970s, as motorcycles grew cylinders and cubic centimeters, welterweight 250cc bikes were increasingly viewed as a transition class as many new riders moved up the capacity ladder to a “real” motorcycle. And that’s a shame, because the enduring charms of many frisky lightweights have become overlooked.
Take the Suzuki GT250 for instance. Developed from the potent and petulant T20 X6 Hustler (also called the Super Six) and the T250 Hustler of 1969-1972, the GT250 matured over its life from a wild child with a penchant for perforating pistons into a mild-mannered sophisticate. Along the way, it lost its performance edge to increasingly restrictive noise and emissions regulations (measured rear wheel horsepower went from 22.3 at 7,500rpm for the 1973 GT250K to just 20.1 for the 1975 GT250M), yet it arguably became a better all-around motorcycle as it matured.
Suzuki’s basic formula was well tried and tested. The 247cc parallel twin 2-stroke used conventional piston porting with two transfer ports and was fed by two 26mm carburetors. The crankshaft ran on three main bearings and drove the 6-speed transmission through a gear primary with wet multiplate clutch and chain final drive. The powertrain fitted into a duplex cradle frame with a twin shock rear swingarm and conventional telescopic fork. Suzuki’s Posi-Force oil injection system took care of engine lubrication from a 1-quart oil tank.
Launched in Japan in 1970, the GT250 arrived in North America for the 1973 season as the GT250K, claiming 31 horsepower, a dry weight of 320 pounds and a top speed of 90mph. New for that year (1972 in Japan) was a front disc brake and Suzuki’s “RAS” Ram Air System — an aluminum plate bolted to the top of the engine intended to direct cooling air onto the cylinder heads. It also helped to make the engine a bit quieter. Styling was revised from the previous year’s Japanese market model, with sharper lines and a new paint scheme.
In addition to helping the 2-stroke twin run cool, the Ram Air System also obscured the rubber inserts between the cooling fins designed to reduce “ringing.” More restrictive carburetor slides and exhaust also reduced overall engine noise, but resulted in a drop in power over the earlier (Japan only) GT250. This same basic specification (but with declining power output, as noted) continued through the 1975 GT250M, but a revised engine arrived for 1976 (GT250A) with four main bearings, four transfer ports and 28mm carburetors in place of the previous 26mm units. The Ram Air System was dropped at the same time, although fin area on the cylinder head was increased to ensure effective cooling. Although it continued in some markets, the GT250 was dropped in the U.S. in favor of Suzuki’s growing line of 4-stroke twins and triples.
As a rider, the GT250 was intended to be less frantic than its competition (principally Yamaha’s segment-leading RD250), and was physically larger, heavier and more comfortable, with less peaky power delivery. It still needed 4,000rpm to get underway smoothly, with a powerband that peaked at 7,500rpm, but it was unassuming and easy to come to terms with. “Charismatic bikes have engines which excite enthusiasts. But motorcycles like the GT250M don’t have those sorts of engines,” Cycle Guide wrote in 1975.
Underscoring the bike’s pedestrian orientation, the GT250’s handling was biased toward straight-line stability, which meant slower steering inputs — appropriate for a bike meant for commuting, not canyon carving. Braking was effective in the dry, but performance of the new disc front brake was compromised by wet conditions. Suspension was considered overly stiff at the rear and generally under-damped. That said, the GT250 could be a relatively comfortable touring machine, as “The Suzuki engine feels as if it could go on forever at 5,000rpm (55mph), where it spins with amazing smoothness. Even the image in the rearview mirror remains unblurred,” Cycle Guide said.
The GT250 also promised (relative) longevity. Its conservative porting generally meant less top end wear, while the quarter-liter bike also borrowed the tranny and many other components from the 315cc T350. In summing up the GT250K of 1973, Cycle noted that, compared with the RD250, “The Suzuki is significantly more comfortable, much quieter, a little heavier, taller, slower, steadier, stops better, and is more composed.” Those were good qualities, qualities that helped the GT250 differentiate itself from Yamaha’s hot 2-stroke twins. By today’s standards 247cc may seem small, but the GT250s were solid and reliable bikes, qualities that, 40 years later, still make them shine.
Yamaha RD250 1973-1975
Claimed power: 30hp @ 7,500rpm (claimed)
Top speed: 95mph (period test)
Engine: 247cc air-cooled reed-valve 2-stroke parallel twin
Weight: 309lb (dry)
Price then/now: $759 (1973)/$1,500-$2,500
The reed-valve RD250 was developed from the 1971 piston-port YDS7, but also borrowed from the all-conquering TD250cc racers. By incorporating a reed valve in the intake, Yamaha was able to use larger ports and more radical port timing without losing low end power. Yamaha also added a seventh “transfer” port that fed mixture directly from the intake to the combustion chamber to aid scavenging. Output went through helical primary gears to a wet multiplate clutch and 6-speed transmission.
All this tech gave the RD250 a power and performance advantage over the GT250. Cycle magazine’s February 1973 comparo gave the RD250 a peak 26.2 horsepower on the dyno compared with the GT250’s 22.3, both at 7,500rpm. And the Yamaha also produced more torque, 19.36 ft/lb versus the GT250’s 15.63. The RD was also lighter, louder (by 3dB — double the sound pressure level!) and slightly more compact, but it lacked the Suzuki’s front disc brake (until the RD250B of 1975). In terms of street performance, the RD was quick, with excellent handling, and braking that was adequate (for the time) from the TLS front drum, though it was called “unpredictable and touchy” during braking tests by Cycle, which pointed to the tires as the problem. Cycle concluded of the RD250: “ … the feeling that projects is one of tightness and mechanical integrity … the Yamaha is hard edged and crisp.”
Kawasaki S1 250cc 1972-1975
Claimed power: 32hp @ 8,500rpm (claimed)
Top speed: 83mph
Engine: 249cc air-cooled 2-stroke triple
Weight: 348lb (dry)
Price then/now: $815 (1973)/$1,500-$2,500
In marketing speak, the S1’s Unique Selling Proposition when compared with the competition was its extra cylinder. In practical terms, though, the S1 engine was really just a sleeved-down S2 350, meaning it had a lot less horsepower to lug around the bigger bike’s frame and cycle parts. The three-pot engine was a conventional piston-port 2-stroke driving the back wheel through a gear primary and 5-speed gear box. Sadly, the S1 never got the S2’s front disc brake: that had to wait until the KH250 arrived in 1976. Nor did it ever get six gears.
And while testers concluded that the S1 presented a considerable improvement in steering (“Kawasaki’s small triples handle extremely well,” Cycle magazine said) and styling over its predecessor, the drum front brake was considered dangerously prone to fade while the performance from the long-stroke 250 was disappointing. Cycle found that it “won’t pull 65mph in fifth into the wind,” while downshifting for more power “brings high RPM shakes.” Cycle’s dyno recorded 23.3 horsepower at 8,500rpm for the S1.
Cycle concluded: “One might think that the poor performance and misbegotten hardware of yesteryear has all been consigned to The Pit … but you’ll find it all in the S1 triple, the fatiguing vibration, indifferent brakes, and modest acceleration — and the feeling that Kawasaki somehow should have done better.” MC