Jet Air System: Operation

Air flows to the jet valve through two intake openings near the carburetor throttle valve, a passage in the intake manifold and a passage in the cylinder head. The intake stroke pulls air into the combustion chamber through the intake valve port and the jet valve opening. When the throttle valve opening is small, a large pressure difference is produced between the jet valve opening and the jet intake opening as the piston goes down. This causes jet air to flow into the combustion chamber at a much higher speed than it does at large throttle openings. Because the jet valve opening points directly at the spark plug, the air stream scavenges gases accumulated in that area. It also produces a swirling action in the combustion chamber which continues throughout the compression stroke. This results in a longer burn period after ignition.