The valve cover is unique to the ‘72 and ‘73 models. A cable goes from a lever on the right handlebar , just below the brake lever, to the compression release that’s built into the valve cover. When you pull the decompression lever it also activates the starter. The decompression mechanism works by pressing down on the end of the left side exhaust valve. 1972 was the first year for the electric starter and the motor was not very powerful. Later models had a more powerful starter, therefore eliminating the need for a compression release.