smta carb frosting

Its 94 with a heat index of 103. Running my SMTA not over half
throttle for about 30 minutes. With tractor running, I got off and
happened to notice the pipe above the carb was frosted and the
pipe was very cold. When I finihed using the tractor and shut it off,
it was still frosting and very cold.
Could somebody explain this to me?
Thanks in advance
Don

That is normal, the air passing through the carb and manifold is traveling so fast that it becomes cold and the moisture in the air forms as frost on the manifole, once the tractor gets to working and the engine is warmed up to operating temp. the frost will melt and not form.

That is the way a carb works and has to do with the atomizing of the fuel which in turn causes things to get very cold. If it does not happen then the carb is not working as it should and you will have other problems. But yep part of life

It is a natural effect from the intake air passing through the carburetor venturi. High humidity makes it worse. Actual temperature has little effect.
It isn't just the Ms that do it as I've seen the same thing on just about ALL makes and models of tractors.

clean your air cleaner and that will help . it's a little warm for frosting , sweating is more like it this time of year.

This is pretty interesting and I never knew this, yesterday it was 102 with a heat index of 117 and I was doing a little work with my M and I noticed this as well. It wasnt frosting up just lots of condensation on the intake and the carb and it was cool to the touch.

It is all about physics and the properties of gasses.

When a gas is compressed it gives off heat. That is why the air exiting an air compressor or turbocharger gets hot. The reverse is also true. When the pressure of a gas is decreased it will take on heat from the surrounding area.

In the case of your SMTA the change in pressure of the air/gasoline mixture takes place across the throttle plate. Air entering the carburetor is at atmospheric pressure, about 29 inches of mercury. The engine is an air pump and the throttle plate is restricting the air flow into the engine. Under low load conditions the vacuum created above the throttle plate is in the neighborhood of 14 - 17 inches of mercury, about one half of the atmospheric pressure below the throttle plate. This change of pressure causes the air to try to take on heat which it gets from the metal of the carburetor and manifold. Given enough time it will cause the temperature of the carburetor and lower intake manifold to become lower than 32 degrees which causes the condensation that has collected there to freeze to become frost.

As the load on the engine increases the vacuum will drop off so that the demand for heat is less, resulting in possible condensation but no frost.

(quoted from post at 17:13:32 08/14/10) That is normal, the air passing through the carb and manifold is traveling so fast that it becomes cold and the moisture in the air forms as frost on the manifole, once the tractor gets to working and the engine is warmed up to operating temp. the frost will melt and not form.

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If the frosting was due to the pressure drop caused by the venturi effect, it would be greater at full load rather than under light load. The greater the load the more air is passing through the venturi causing a greater difference pressure.

As the velocity of air is increased, the temperature will decrease. On aircraft you apply carburetor heat to prevent ice build-up. Tom

Happens all the time during days of high humidity. mike

Frosting and sweating of these carbs is typical. My F-20 does it big time, and so does my H. In fact, I find the more humid it is, the more they frost up. The heat capacity of humid air is pretty high, so when the air mixture drops in the venturi, along with the fuel vaporization, these puppies cool down fast.

I have to admit, the first time I saw it, i was alarmed and puzzled. After I thought about it, and did some research, I found out that it was very very normal. I definately would not lose sleep over it......in fact, I don't. :wink: