On my TimberKing with the onset of colder days I get ice build up on the carburetor. It's a 27hp Kohler V twin. On some of the smaller Kohler they have a heater kit for the carb but not mine.
Does anybody else have that problem or know of a fix?
Have to expand a couple of things here so there is a complete understanding of what is going on when a carburetor "ices" up.
The venturi causes air to 'speed up" and pressure to drop as it passes through and this is what draws fuel from the metered orifice in the carburetor throat. When the engine stops, the air flow stops and fuel is not drawn out of the metered orifice. If a float "sticks", this is where fuel drips out, or floods an engine. If a float level is set too low, then the pressure differential will not draw fuel through the metered jet and will not run, or will only run with the choke out, caused the engine to draw hard on the intake, but not achieve a proper fuel/air mixture of 18 - 1 for optimum fuel burn. excess fuel causes an actual loss of power, and smoke indicates you are not getting a good burn in the combustion chamber.
Quick lesson over.
When humidity is high, meaning the air is carrying a lot of moisture, or close to saturation (like rain), then one other aspect comes into play: When the speed of air increases and the pressure decreases in the venturi of the carburetor, the temperature will drop.....now, if it is 80 degrees outside and 50% humidity, no big deal...a little water vapor that condenses in the fuel air mix actually increases power and cools the cylinder head temps....meaning you have a touch more efficiency in the power range.....some of you may know that older tractors, and I mean 30s and older, like the old D John Deere, had an actual meter valve that allowed the operator to open and add water to stop detonation and gain power when advancing timing lead.
Now to the other side of the coin: When conditions are right, and I mean it can happen at 60 degrees and a sunny day, there may be enough temp drop to cause ice to form in the throat of the carburetor, thus you have restricted air flow, engine runs rich as it dies off. Usually this condition happens when there is visible moisture, like rain, fog, or it feels damp outside and never happens below freezing temps.
In aircraft engines, (one of my trades is A&P, as well as a pilot) there is a "box" that surrounds the intake side of the carb, between the air filter and carb intake, that allows the pilot to select "carb heat". In icing conditions, or when ice can form, a pilot can add carb heat as needed. All or a little. The head is drawn from a shroud around the exhaust pipe.
The down side of adding heat is that as air is "warmed" or heated, it is less dense. This changes the fuel air mixture. More fuel and less air, since hot air expands. That is why carb heat, or warming the intake air is not done as a matter of convenience. Most engines with a top mounted intake generally do not suffer from carb icing because heat from the engine warms the carb and ice crystals pass through without sticking, but in cold weather, and a single carb on an intake pipe isolated from the engine will ice.
So the solution for you guys having this issue to make a sheet metal shroud that you can shift intake air from around the exhaust pipe or maybe catch cooling air from the head and guide it into the intake air stream. You can introduce it before the air cleaner and this will eliminate carb ice.
BTW, air and fuel mixtures are not based on volume....to understand why you don't use heated air all the time is basic. Fuel produces X amount of power based on weight combined with X amount of air, also based on weight. Air density decreases as you increase altitude, and that is why engines develop less power the higher you go, and you have to adjust the air screw mixture or metering when you change elevations...pilots do this on carburetored engines with a mixture control, and fuel injection does this automatically.....that is why this phenomenon is unique only to carburetors.
