its inside the rectangular opening in the picture. his one doesnt have the fuctionality. So its not drilled out for it>>
caused by excessive fuel vapors during hot engine operation.

The compensator consists of a thermostaticallycontrolled valve, a heat sensitive bi-metal strip, and a valve holder and bracket. The compensator valve assembly is held in place by a dust cover over the valve chamber. A seal is used between the compensator valve and the float bowl casting. The valve closes off an air channel leading 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 offset the enriching effects of these 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 the extra air is not needed, the bi-metal strip relaxes, closes the valve, and operation returns to normal mixtures.

For proper idle adjustment when the engine is hot, the compensator valve must be closed. To check 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.