Years produced: 1982 (U.S)
Power: 7hp @ 6,000rpm (claimed)
Top speed: 53mph (period test)
Engine: 49.5cc air-cooled 2-stroke single
Transmission: 5-speed, chain final drive
Weight/MPG: 187lb (dry)/65-75mpg
Price then/now: $798/$800-$1,500
How can an engine of only 50cc (just 3 cubic inches!) make enough power to set an average speed of over 85mph on the Isle of Man TT circuit? In 1965, Ralph Bryans did just that on the 50cc, double overhead cam Honda RC115, securing both the rider’s and manufacturer’s ultra-lightweight world championship, the little twin revving to 20,000rpm to produce its 15 horsepower. So don’t dis small bikes!
It wasn’t a double overhead cam twin that Honda presented to U.S. buyers in 1982, however, but a simple 50cc 2-stroke. It still produced the pulling power of seven horses — just not in quite the same way. In torque-obsessed America, Honda was facing an uphill sales battle with the MB5 — but it was a remarkable motorcycle, and is now a rare and sought-after classic.
Essentially similar to the European market MB50 produced between 1979 and 1988, the MB5 was sold in the U.S. for one year only. Inside its smart black engine cases was a 49.5cc reed-valve 2-stroke with a balance shaft and 7.6:1 compression ratio producing 7 horsepower at 6,000rpm.
Engine lubrication was by oil injection, while the separate transmission ran in oil. Straight-cut primary gears drove the wet multiplate clutch and 5-speed gearbox. A 16mm Keihin carburetor fed fuel, with sparks handled by a contactless CDI unit. A 12-volt 66-watt alternator provided power for the lights. No electric start was offered, just a kickstarter.
The ingenious frame used a tubular spine, with a pair of straight tubes welded to the headstock running back either side of the spine down to the rear frame tubes, triangulating the frame. The engine hung from the spine and was clamped at the back between two plates welded to the rear down tubes, which also formed the swingarm pivot.
A telescopic fork and dual rear shocks gave 5 and 3.5 inches of travel, respectively, and ran on a pair of Honda’s ComStar composite three-spoke wheels with 2.5 x 18-inch tires. A single 8.6-inch front disc and rear drum brake provided stopping power.
The MB5 was outfitted with all the equipment of a full-size motorcycle, including matching speedometer and tachometer, dashboard warning lights, and a full set of lights and turn signals. The result was a fully featured miniature masterpiece. But what was it like to ride?
Cycle magazine tested the MB5 in late 1981 and found that the Honda “accelerates, stops and rides much better” than other 50cc motorcycles and mopeds they had tried. “The MB5 feels much less toy-like and it handles like a regular motorcycle, albeit a small one,” Cycle said. And while the steering was quick, the MB5 also had good directional stability.
Performance was “leisurely, to be kind,” said Cycle, “unless the full rev range was used,” when the MB5’s acceleration to 40mph was “quicker than some of today’s more plebeian automobiles.” It was capable of getting to and holding 45mph “as long as you keep the engine buzzing as you shift through the gears.”
Cycle World took the MB5 to the strip, recording 22.7 seconds at 51mph for the standing quarter with a flying top speed of 53mph.
No passenger pegs were fitted to the MB5, in line with the GVWR maximum load capacity of 220 pounds. However, Cycle did the “real world” sums and found this worked out to less than 150 pounds with a full tank. At close to 200 pounds suited up, though, their tester had no problem with suspension bottoming.
Fuel consumption seemed high for its class at 65-75mpg, rather than the 100mpg toted for most mopeds, though the tester admitted to a “ham-fisted riding style.” That said, the generous 2.4-gallon gas tank was good for a 160-mile range. As for oil, the MB5 used less than a quart in Cycle World’s 700-mile test.
Though admitting that it was a town bike intended for easy, fun, urban transportation, Cycle World said the MB5 was “a fully modern machine, offering all the advances made in motorcycling over the last 20 years.” MC
Contenders: Sub-100cc rivals to Honda’s MB5
1982 Kawasaki AR80
Years produced: 1982 (U.S)
Power: 10.2 hp @ 8,500rpm (claimed)/75mph
Engine: 78cc air-cooled 2-stroke single
Transmission: 6-speed, chain final drive
Weight/MPG: 165lb (dry)
Like the MB5, the AR80 was only sold in the U.S. (alongside the 50cc AR50) in 1982 — and is perhaps even rarer. Its 78cc air-cooled, reed-valve, 2-stroke single used an 18mm Mikuni carburetor and CDI ignition. Lubrication was by Kawasaki’s Superlube injection system. The engine drove a 6-speed transmission by gears and had a chain final drive. The tubular, double-cradle frame ran on Enkei alloy 18-inch wheels wearing 2.50 front and 2.75 rear tires with telescopic fork front and Kawasaki’s Uni-Trak single-shock swingarm rear suspension. A single front disc and rear drum brake provided stopping.
With its more powerful 80cc engine in what was essentially the same running gear as the smaller-capacity AR50, the AR80 was “a manic little machine,” says mopedarmy.com, noting that it was capable of performing as well as, or even outperforming, most 125cc machines of the time. There’s also a thriving aftermarket tuning parts supply, with performance parts up to and including liquid cooling for the AR80 … if you can find one!
1979-1982 Puch Magnum 50
Years produced: 1979-1982 (U.S)
Power: 2hp @ 5,000rpm (claimed, Magnum MkII)/30mph
Engine:48.8cc air-cooled 2-stroke single
Transmission: 2-speed/pedal assist
Weight/MPG: 129lb (dry)/150mpg (claimed)
Unlike the MB5 and AR80 “nopeds,” the Magnum was a true moped with pedals for starting and uphill assistance, and with its meager power, these were more than an afterthought! Magnums were sold in the U.S. with both single-speed and 2-speed automatic transmissions, oil mix and oil injection, steel or mag wheels, and with or without a speedometer dash.
Perhaps most desirable was the final, limited-edition Magnum MkII “LTD” of 1981-1982 with the 2-speed transmission, 17-inch mag wheels, oil injection, speedo, keyed ignition and turn signals. The Magnum’s drivertrain hung beneath the characteristic “banana” frame with chain drive, telescopic forks and a twin shock swingarm. The 50cc air-cooled, 2-stroke engine featured a 14mm Bing carburetor and Bosch 6-volt flywheel magneto.
The Magnum also lent itself readily to tuning, and enterprising owners have managed to squeeze several times the stock 2 horsepower from the engine.
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