2004 SR Johnson 4 Stroke 9.9-15HP Outboards Service Manual, Page 149Get this manual
POWERHEAD DECOMPRESSION SYSTEM
DECOMPRESSION SYSTEM
Decompression system activates by means of the centrifugal system installed on the exhaust camsWhen starting, decompression cams lift the rocker arms and open the exhaust valves slightlyOnce the engine starts, centrifugal force closes the decompression cams, thereby returning the exhaust valves to the normal closed positionThe exhaust valves normally closed the decompression cams by centrifugal operation