Early Fuel Evaporation ( EFE ): Description and Operation

Fig. 67 Heated Intake Air System:

OPERATION

The heated intake air system allows the carburetor to be calibrated leaner than would ordinarily be possible to reduce CO and HC emissions during warm-up, improve cold engine driveablity, and reduce carburetor icing. The air cleaner includes a valve to regulate the mixture of warm and cold air entering the carburetor. The air valve is operated by a vacuum motor controlled by a bi-metal thermo sensor.

Fig. 68 Operation Of Heated Intake Air Sys. (Air Cleaner Temp. < 30 Deg. C Or 86 Deg. F):

When the air inside the air cleaner is cold (less than 30 degrees C or 86 degrees F) the bi-metal thermo sensor remains air tight. Full intake manifold vacuum signal is applied to the vacuum motor holding the air control valve to the full heat position. Warmed air from the heat cowl enters the carburetor without mixing with cold air.

Fig. 69 Operation Of Heated Intake Air Sys. (Air Cleaner Temp. > 45 Deg. Or 113 Deg. F):

When the air inside the air cleaner is hot (greater than 45 degrees C or 113 degrees F) the bi-metal thermo sensor is fully open venting the manifold vacuum signal. No vacuum signal is applied to the vacuum motor so the spring inside the vacuum motor moves the air valve to close off the heated air duct. Cold air from the engine compartment enters the carburetor without mixing with warm air.

Fig. 70 Operation Of Heated Intake Air Sys. (Intermediate Air Cleaner Temp.):

When the air temperature inside the air cleaner is warm (between 30 and 45 degrees C or 86 and 113 degrees F) the bi-metal thermo valve is partially open modulating the vacuum signal to the vacuum motor. The air control valve operates in mid-range mixing warmed air with cold air to produce an acceptable intake air temperature into the carburetor.