The 660 engine incorporates a five-valve cylinder-head. There are three intake and two exhaust valves. The theory is that the smaller valves have a larger area at a lower weight than a four valve system and allow maximum intake flow and velocity.
A vacuum operated fuel pump is mounted on the bottom of the fuel tank to lift the contents of the tank to the twin carburetors.
The fuel system incorporates one slide carb and one butterfly carb. These are operated sequentially by a manually adjustable system.