I have a J230D with a 3300A engine. When I do my run-up checks and apply carb heat there is no change at all to engine RPM. I have checked the operation of the carb heat mechanism and it appears to be working ok. Is this normal? I am used to Cessna aircraft where you certainly get an RPM drop with the application of carb heat.
Yes some Rpm drop with carby heat is normal. It should be about 20 or 30 rpm at 2000rpm, so you have to watch carefuly.