106. During the run-up at a high-elevation airport, a pilot notes a slight engine roughness that is not affected by the magneto check but grows worse during the carburetor heat check. Under these circumstances, what would be the most logical initial action?

When carburetor heat is applied, the air/fuel mixture of an engine will be enriched because any given volume of hot air is less dense than cold air of the same volume. This condition would be aggravated at high altitude where, because of decreased air density, the mixture is already richer than at sea level.