Fuel Control
Some models are equipped with a Holley 6550 carburetor. This model contains an electrically operated oxygen feedback solenoid. This solenoid meters the main fuel system of the carburetor and operates in parallel with conventional fixed main metering jets. The computer controls operation of the solenoid in response to signals received from data sensors, particularly the oxygen sensor. See Fig 1 .
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 conditions by controlling the amount of time that the solenoid is energized and de-energized. The computer controls the duration of time that the solenoid is energized in comparison to total time of solenoid operation and in response to engine operating conditions and/or oxygen sensor signals. In this manner, the ideal air/fuel ratio can be constantly maintained.