Carb heat
My aircraft has a Lycoming O-235 which, legend has it, is prone to carb icing. I therefore give it a blast of hot air about every 10 minutes in this weather. Typically today Stansted were giving 6 degrees with a dew-point of 4 degrees. So cruising revs of 2450 set, blast of carb heat for 30 seconds, revs drop to 2350, no coughing and banging, push in carb heat knob and the revs only return to 2410 or thereabouts. It always happens....why?