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?
Hot air less dense than cold, therefore less power, therefore RPM drops.
RPM drop is a the check for carb heat working properly, so that's good. Try keeping it hot for a couple of mins and see if it recovers to 2450 - if so, you had a little ice and the carb heat needed more tim eto totally clear it, if not, its just a quirk of your aircraft .... and they all have theor own little ways .
Just keep setting it to ''on'' and checking, it's good practice