One-Year Wonder: 1982 Honda MB5

Comparing the Honda MB5 with its sub-100cc competitors, the Kawasaki AR80 and Puch Magnum 50.


| March/April 2017



1982 Honda MB5

Motorcycle Classics archives

Honda MB5
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.





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