Non-return valve for headlights

[jimj]

If there was no non-return valve from the intake manifold to the vacuum pipe for the headlights, would it affect the carburation?
Jim

[Grizzly]

Not tried it but as the idle jets (Idle and progression) is vacuum based i'd say it would increase the volume of the inlet making accelerating through the progression on that one cylinder much leaner initially, not sure it would effect the cruise though. The one way valve should stay shut most of the time as it should hold the peak vacuum which is achieved when accelerating and snapping the throttle shut (overrun).

I'd guess you would get a similar effect as an air leak, not sure the headlight pods would work that well either as most of the vacuum they need is achieved on the overrun.

[69S4]

On my Stromberg S4 it makes no discernible difference at all whether there's a non return valve in the headlamp line - to the engine anyway. It makes a substantial difference to how the headlamps stay up. Your Weber mileage may vary as they say.