CLASSIC IRON: 1970 KAWASAKI G31M 100 CENTURION BABY GREEN STREAK

July 2, 2013
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In the late 1960s, the 100cc class was booming with a multitude of brands filling the starting lines. Kawasaki had previously dabbled in the offroad world with less than stellar results, using mostly modified street bikes. That changed in 1970 when they released the G31M Centurion, and soon left everyone else in the dust. If you went to any 100cc TT (Tourist Trophy) or flat-track event in 1970 or 1971, you would see G31M riders on the podium. Top-notch suspension, refined handling and a good pedigree? Nope, just power!

The “Baby Green Streak,” as it was often called, put out an astounding 18.5 horsepower at 10,250 rpm from its rotary disc valve engine. This was nearly double what the Hodaka 100s of the time produced. The stinger on the expansion chamber gave the Centurion a distinct sound that is unmistakable to this day. The engine case was slightly different from other Kawasakis, with the G31M having a secondary air intake on the carburetor cover. It also required the use of bean oil as a fuel additive for lubrication. Even then, lower-end life was short because of the engine’s high rpm. Never pretending to be anything but a track bike, the G31M came with smooth Dunlop K70 3.25-18 tires front and rear.

Norm Bigelow, a factory Kawasaki employee for 30 years, was one of the riders who modified the original G31M for motocross: “We used a CZ plastic tank and fenders, replaced the highly tuned cylinder with a mildly ported G4TR cylinder, and raced it with some success in the 100cc Novice class at Saddleback Park. Soon the Japanese 125 era started, and the 100 class slowly disappeared.”

1970 KAWASAKI 100 CENTURION FACTS

WHAT THEY COST
Retail price in 1970 was $560. Actor Steve McQueen was given six G31Ms by Kawasaki for the filming of the motion picture LeMans. McQueen kept one for himself, painted it orange with gold stripes and gave it the name “Ringadingdoo!” The bike sold at an auction in 2007 at the Petersen Museum in Los Angeles for an unheard of price of $55,575. $7000 for a good one is more realistic.

WHAT TO LOOK FOR
The 1970 model had polished aluminum fenders, and the 1971 model came with painted fenders that matched the tank. The gas tank’s lime green and white design originated with California painter Molly. The stock pipe is important for collectors. It is important that the engine runs, because these things were “time bombs,” and engine parts are hard to find. It would be a huge bonus to find the hang tag with dyno results (included with every machine) done at the factory.

PARTS SUPPLY
Parts are scarce! Try Dave Boydstun at AMS Racing in Mesa, Arizona, at www.amsracing.com and by phone at (480) 610-4574.

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