Frosty carb-

Have noticed my 8N carb frosting up a bit the past few weeks on cooler days. I expect it to frost up today because it will not get above 32 degrees. It eventually goes away. Did not notice this on the 2N. Could this be because of the different kind of carb on the 8N? Any thoughts are welcome.
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Mr. T. Minnesota

Frost happens when the air temperature is near freezing, but not much below. Experts will tell you that it can't happen when the air is below freezing, because the moisture will already be frozen.

There are two types of carburetor frost, exterior and interior. The exterior frost happens when the cooling effect of the air drawn through the carb chills it enough below freezing that the moisture drawn from the surrounding air condenses on the surface and freezes there. The outside surface of the carb has to be somewhat below freezing for this to happen.

Interior frost can happen at a higher temperature than the exterior frost. This is because the air flowing through the venturi cools as it speeds up as it passes through. This draws heat from the air and the surrounding parts of the carb, cooling them below freezing and allowing the ice to build up, sometimes to the point of killing the engine when the carb quits working.

The intake manifold is designed to transfer some of the heat from the exhaust manifold to the carburetor to help combat this, but it can't overcome it all the time. The original cast iron carburetors help transfer this heat and hold it better than the pot metal kind.

Frost on the outside of the carburetor doesn't affect anything, but it may indicate that the venturi is being exposed to icing conditions.

Make a "carb heater" out of tinfoil to get some manifold heat to the carb.
75 Tips

Would you believe if it did not happen then the carb is not working as it should. Simple fact is that as the gas gets atomized it also gets very cold so yep the carb will frost up simple physic's and in a car or truck with a carb it would do the same thing is it was not for the hot air intake off the exhaust manifold. Same thing happens with compressed air. As it is compressed it gets hotter but as you let it back out like with an air blow gun it gets colder and if you where to hold that blow gun at the same place long enough it would also frost up where it was hitting

I have had air impact wrenches that froze up using them in cold weather .

Old,
The energy needed to change a liquid to a gas is called heat of vaporization. Gasoline is like freon, change it's state from a liquid to a gas removes energy from it's surrondings, cold carb, frost.
George

I have and always have heard the term atomizing so that is what I use when talking about what and how a carb works so I will keep doing so since that is what I was taught and I learned that 40 plus years ago

Yep and that is a combination of problems. #1 you have water in your air system so you need an air dryer. #2 that is also normal since as you decompress air it cools and in doing so yep it can cool to the point of freezing and you can even give your self a frost/freeze burn using compressed air

Carburated airplane engines have a method to cause the carburetor to draw in heated air... the control knob is called... CARB HEAT!!

The process of fuel atomization can cause the fuel/air mixture temperature to drop as much as 100 degrees. So you might imagine there is a wide range of ambient temps where carb icing may occur.

Ice formation INSIDE the carb usually causes a rich mixture.... and can get so rich the engine dies. This often causes distress for PILOTS... and can irritate tractor drivers, too.

It"s normal.

The evaporation of fuel in the carb cools the mixture and below ~ 50 °F, and if the humidity is high enough, the wall temperature in the carb will drop below freezing and exterior frost can be seen. Frost can also form in carb venturi (from the humid air), and over the transition port and butterfly and mess up the mixture control. It might run ratty until the manifold heats up enough to prevent this. It"s a problem with leaner mixtures so Detroit added the heated intakes on engines in the late "60"s and early "70"s when the first emmission controls came in on cars. Adding Heet additive to the fuel will not prevent this only a heated intake will. That"s why aircraft engines have carb heat. It"s obviously more critical for them.