Rotary-Valve Rocket: 1969 Kawasaki 350 Avenger A7SS

1 / 11
1969 Kawasaki 350 Avenger A7SS
1969 Kawasaki 350 Avenger A7SS
2 / 11
1969 Kawasaki 350 Avenger A7SS
1969 Kawasaki 350 Avenger A7SS
3 / 11
1969 Kawasaki 350 Avenger A7SS
1969 Kawasaki 350 Avenger A7SS
4 / 11
The A7SS' Signature twin high pipes make the bike look longer than it really is.
The A7SS' Signature twin high pipes make the bike look longer than it really is.
5 / 11
1969 Kawasaki 350 Avenger A7SS
1969 Kawasaki 350 Avenger A7SS
6 / 11
The A7SS’ signature twin high pipes make the bike look longer than it really is.
The A7SS’ signature twin high pipes make the bike look longer than it really is.
7 / 11
The A7SS’ twin-leading-shoe 7-inch front drum was considered a real performer in its day.
The A7SS’ twin-leading-shoe 7-inch front drum was considered a real performer in its day.
8 / 11
1969 Kawasaki 350 Avenger A7SS
1969 Kawasaki 350 Avenger A7SS
9 / 11
The Avenger A7SS manages to look compact and husky at the same time. It was also a real performer: The mechanically identical street version could run the quarter mile in 14.35 seconds.
The Avenger A7SS manages to look compact and husky at the same time. It was also a real performer: The mechanically identical street version could run the quarter mile in 14.35 seconds.
10 / 11
The Avenger A7SS manages to look compact and husky at the same time. It was also a real performer: The mechanically identical street version could run the quarter mile in 14.35 seconds.
The Avenger A7SS manages to look compact and husky at the same time. It was also a real performer: The mechanically identical street version could run the quarter mile in 14.35 seconds.
11 / 11
Rotary-valve design makes for a wide engine due to the placement of the carbs under covers on either side of the crankshaft.
Rotary-valve design makes for a wide engine due to the placement of the carbs under covers on either side of the crankshaft.

For Japanese motorcycle manufacturers, the 1960s were like the early 1900s for U.S. car companies, with bike makers eager to license, adapt or invent new technology to make their products stand out and attract buyers in a rapidly expanding marketplace.

During this growth period, most Japanese companies focused on 2-stroke engines. Simpler and cheaper to build than 4-strokes, they also offered smaller and lighter packaging, and better performance for the displacement. As well, in the 1960s there were no regulations that particularly affected relatively dirty-running 2-strokes, which gained plenty of notoriety due to their attendant mosquito-fogging trails of blue smoke. Building “‘strokers” became the accepted industry-wide means of delivering the power that customers wanted, and all the major players except Honda focused on developing them. Honda may have eventually enjoyed the last word on the matter, but even so, 2-strokes held on until the early 1980s.

Rotary valves: genius or enigma?

One of the most flamboyant of those 1960s 2-stroke engineering companies was Kawasaki. Its range included rotary-valve induction singles and twins such as the lovely 1969 350 Avenger A7SS twin seen here. And they were fast. Until the arrival of the vaunted Kawasaki H1 500cc triple, virtually nothing else on the street — regardless of displacement — could dispatch the Avenger in a quick stoplight fight.

Kawasaki’s rotary-valve engines are traditional 2-strokes with the exception that they use a spinning disc valve, mounted on the crankshaft in between the side-mounted carburetor and the crankcase, to control the intake timing. Looking like a phenolic pizza cutter with a big piece missing, the whirling disc sweeps across an opening in the side of the crankcase, first exposing and then chopping closed the portal at precise intervals. The carburetor or carburetors mount outside of the sealed rotary-valve housing on one or both sides of the engine.

  • Published on Aug 15, 2014
Comments (0) Join others in the discussion!
    Online Store Logo
    Need Help? Call 1-800-880-7567