Mono
Doubtless you're right about the carb heat but you might want to check the cable anyway. Reading your account of the 3/4 inch of travel reminded me that I once had a 'flat spot' on the carb heat (O-320) which defied engineer inspection and finally gave way somewhere over the Western Approaches, fortunately to 'hot'. Wouldn't have been so funny if it had been the throttle. The little pinch bolt in the butterfly arm had been stripped by constant engineer meddling. The problem (the cable slipping) only happened with the engine hot, hence they never found it.