Frequency Valve

Frequency valve (feedback solenoid) has 2 operating positions. Valve is either open or closed once each duty cycle. Pulse solenoid in valve makes 10 cycles per second. Dwell meter is used to measure duty cycle. Duty cycle reading is opposite of fuel injected systems so 90° is full lean setting.

In low speed or idle circuit, frequency valve regulates air pressure above idle jet. This changes pressure differential between air in float bowl and air above idle jet. When valve is open, more air flows through feedback circuit and reduces "vacuum signal" at idle jet. This reduces amount of fuel pulled through idle jet, resulting in leaner mixture.

In partial throttle operation, high vacuum in venturi draws fuel/air mixture from high speed discharge nozzle. Amount of fuel is governed by position of metering rod and by difference in air pressure between nozzle tip and high speed well. Frequency valve changes air pressure in high speed well. When valve is open, increase in volume of air reduces "vacuum signal" to well and less fuel is drawn through high speed circuit.