Hi Fred
The Lycoming engines have the intake tubes inserted through the oil sump with the carburetor mounted on the bottom of the sump assembly. I think the carburetor and the lower intake pipes get a little preheat off the warm oil in the sump, and it helps a little to prevent the carb ice from forming. Its still possible to get ice but I would limit carb heat usage to engine roughness like the manual says. (I’d lean the mixture if I did use carb heat, because the carb heat makes the fuel air ratio way too rich, and it might foul the plugs if you don’t lean to compensate for it.)
