Kawasaki was the last of the big four Japanese manufacturers to start making motorcycles. In 1960 it bought a share in the Meguro motorcycle company that since the 1930s had made four-stroke singles up to 500 cc and later twins up to 650 cc for the Japanese and south-east Asian markets. From 1963 Kawasaki took complete control of Meguro, and the Meguro model K 500 cc four-stroke parallel-twin was re-badged as a Kawasaki. The Kawasaki W1 650 cc four-stroke twin was developed from the Meguro K series, which Meguro had developed from a BSA A7 under license. Kawasaki developed the lighter Kawasaki A1 Samurai in 1966. It was quickly followed by the larger bore model, the A7 Avenger, which is similar to the Samurai. Sharing all of the Samurai components aside from pistons, piston rings, different mufflers with reverse cones, it also featured a race developed oiling system called Injectolube. Oil was not only injected in with the petrol as on the 250 but was also fed to the main bearings. The crankcases and crank were also redesigned for use with the Injectolube system. The A7SS Avenger has a crossover dual exhaust mounted on the left side and just below the seat. Other than exhaust system, there were no other changes between the standard A7 and A7SS.
Engine
The engine was advanced for its time, with features normally seen on race bikes: two-cylinder, two-stroke, air-cooled, oil injected, dual rotary valve. While other manufactures had utilised the advantages of rotary disc valve induction on small single-cylinder machines, only Kawasaki and Bridgestone produced twin-cylinder machines. Rotary disc valve induction ensures that the all the fuel charge is used and not partly lost. As a result, it produces more power, more torque at low revs and better response throughout the rev range. The engine's initial air supply began in an air filter canister below the seat and was drawn through a large plenum chamber just above the transmission and behind the cylinder head, then down into the internal passages leading to the carburetor housing feeding the carburetors. The A7 Avenger had two Mikuni carburetors located on the engine's left and right sides and in line with the crankshaft. The carburetors were enclosed and protected from the elements by carburetor covers fixed to the crankcase. Inboard of each carburetor, and supporting each carburetor, was the disc cover. The rotary disc valve was housed inboard of that cover. In 1969 the ignition system was equipped with a capacitor discharge ignition including thyristor-based switching system then increased the voltage to between 25,000 and 30,000 volts reducing the unburned fuel mixture within the cylinders. During the development of the Kawasaki H1 Mach III, engineers considered using the Avenger's twin-cylinder engine bored out to create the new 500 cc two-stroke power plant as called for in the N100 Plan.
