XJ-S V12-5.3L (1982)
Overrun Valve: Description and Operation
Fig. 10 Overrun valve location and exploded view
These valves were fitted only up to engine number 8S64244.
An overrun valve is fitted to each intake manifold. At high RPM, when throttle is closed, overrun valves open and supply extra air to engine causing
lean mixture.
Some 12 cylinder engines are equipped with overrun valves mounted to the front of each intake manifold. The valves are designed to open during
periods of high intake vacuum. This process serves to maintain a combustible mixture at all times.
