The hot idle compensator is located in a chamber at the rear of the carburetor float bowl adjacent to the secondary bores. Its purpose is to offset enriching effects caused by excessive fuel vapors during hot engine operation.

The compensator consists of a thermostatically controlled valve, a bi-metal strip which is heat sensitive, a valve holder and bracket. The valve closes off an air channel which leads from a hole in the top of the air horn, just beneath the air cleaner, to a point below the secondary throttle valves.

Normally, the compensator valve is held closed by tension of the bi-metal strip. During extreme hot engine operation, excessive fuel vapors entering the engine manifold cause richer than normally required mixtures, resulting in rough engine idle and stalling. At a predetermined temperature, when extra air is needed to offest the enriching effects of fuel vapors, the bi-metal strip bends and unseats the compensator valve. This uncovers the air channel leading from the valve chamber to the point below the throttle valves. This allows enough air to be drawn into the engine manifold to offset the richer mixtures and maintain a smooth engine idle. When the engine cools and extra air is not needed, the bi-metal strip closes the valve and operation returns to normal mixtures.

The compensator valve assembly is held in place by the dust cover over the valve chamber. A seal is used between the compensator valve and the float bowl casting.

In order to ensure proper idle adjustment when the engine is hot, the compensator valve must be closed. To chekc this, a finger may be held over the compensator air inlet channel located on top of the air horn. If no drop in engine RPM is noted on a tachometer, the valve is closed. If the valve is open, plug the hole or cool engine down to a point where the valve automatically closes for proper idle adjustment.

NOTE: Plug the compensator hole with a pencil or something that will be seen, as the plug must be removed before the air cleaner is installed. Otherwise the compensator will not function if the plug is left in the hole.

NOTE: On some applications the air inlet to the hot idle compensator is located beneath the air valve in the secondary bores. The compensator valve can be checked for proper closing by pushing inward on a spring loaded plunger mounted at the idle compensator cover. The idle adjustment procedure is the same as recommended previously.

On some model 4MV carburetors, the hot idle compensator is located on the primary side of the float bowl, it is mounted in the bowl with a pin protruding through the air horn casting to facilitate closing the valve when the idle adjustment is made.

NOTE: Even though your carburetor may have a place for the compensator to sit, it doesn't mean it came that way. It was used on vehicles with air conditioning.