Fuel Control

All models are equipped with feedback carburetors which contain an electronically operated duty cycle solenoid. This solenoid meters air flow of the carburetor fuel circuit and operates in parallel with the conventional fixed main metering jets. The computer controls the operation of the solenoid with electrical signals, in response to input from data sensors. See Fig 1 and Fig 2 .

Fig 1: Cross Sec., Carter BBD Feedback Carb. W/Duty Cycle Solenoid This is a view of the low speed circuit.

Fig 2: Cross Sec., Holley 6145 Feedback Carb. W/Duty Cycle Solenoid This is a view of the idle circuit.

When the solenoid is de-energized by the computer, the solenoid valve spring pushes upward through main system fuel valve. When de-energized, the solenoid main metering orifice is fully uncovered, providing the richest mixture for any given air flow.

When the solenoid is energized by the computer, the solenoid main metering orifice is fully sealed. This solenoid position offers the leanest mixture within the carburetor for any given air flow.

Main system fuel may be regulated between richest and leanest mixture conditions by controlling the amount of time that the solenoid is energized and de-energized. The computer controls the duration of time that solenoid is energized in comparison to total time of solenoid operation.

This duration of time is determined by engine operating conditions and/or oxygen sensor signals. In this manner, the ideal air/fuel ratio can be constantly maintained.