Carburetor heat

This prevents ice from forming around the throttle plate but does not draw large amounts of hot air into the engine as carburetor heat does.

A fixed-pitch propeller aircraft will show a decrease in engine RPM, and perhaps run rough, when carburetor ice has formed.

[1] It must be kept in mind that the ingestion of small amounts of water into the engine following melting in the carburetor may cause an initial period of rough running for as much as one or two minutes before the power increase is noted.

However, more than one pilot, when confronted with a rough running engine has mistakenly turned the carburetor heat back off, thereby exacerbating the situation.

Applying carb heat as a matter of routine is built into numerous in-flight and pre-landing checks (e.g. see BUMPH and GUMPS).

In cars, carburetor heat may be controlled automatically (e.g. by a wax-pellet driven flap in the air intake) or manually (often by rotating the air cleaner cover between 'summer' and 'winter' settings), with use both of "heat stove" type systems, and electric-filament booster elements directly attached to the carb or TBI module.

However, this is not always sufficient, and some automobiles have a history of temporary engine failure during rain or snow conditions (power output drops below that sufficient to continue propelling the vehicle, or even to prevent stalling whilst unladen, and the car cannot be driven/engine restarted until it has stood awhile without a mass quantity of cold, wet air travelling through it, so that the residual engine heat can melt the accumulated ice).

On a few of their air cooled motorcycles, Ducati have utilized an oil line to warm the base of the carb which is operated by the rider via a small valve.