Anti-Backfire Valve: Notes
When throttle is closed suddenly, carburetor air is shut off instantly but fuel flows momentarily which results in a rich mixture. To eliminate backfire, anti-backfire valve opens momentarily to allow air from air pump to enter intake manifold and lean mixture. Opening of valve is triggered whenever there is a rapid rise in intake manifold vacuum. Opening of this valve also prevents rapid reduction of engine RPM which assists in eliminating the need of a dashpot.