Sweaty Carb

H. Springs · Jul 12, 2009

My 706 tractor won"t run more than a minute at a time. I have good fuel flow and have cleaned carb repeatedly. The strange thing is that the top part of the carb is sweating like crazy. Is it possible for me to have icing problems on a 90 degree day? Is this caused by some adjustment that I missed?

Allan in NE · Jul 12, 2009

Ya didn't put that venturi in upsidedown, did ya?

Allan

Red Mist · Jul 12, 2009

Yes - they'll sweat some the first few minutes they run - even here, way down south. Normal behavior.
mike

Jeff Z. · Jul 12, 2009

The gas is cooler than the outside air temperature. This will make the metal sweat.
Same with toilets in the hot summer months.

TomH in PA · Jul 12, 2009

Have you replaced the condensor in the distributor lately? A bad one can show the same symptom.

old · Jul 12, 2009

Only a minute?? Will it restart right away or do you have to wait a few minutes. Do you have a good blue white spark or is it yellow??? Will your spark jump a 1/4 inch gap?? From what you say it sounds more like a spark problem then a carb problem

Anonymous-0 · Jul 12, 2009

The sweating is due to the vaporization process of the fuel and humidity in the air. As anything changes from liquid to a vapor it draws heat from somewhere so carb get cold and moisture condenses. May not be the pure scientific explanation of the process but that is the point of it anyway. Also, the better it vaporizes, like with a leaner mixture or better venturi system the more they sweat and if right outside air temp, freeze up. As far as running a minute, sounds like fuel supply into carb problem.

H. Springs · Jul 14, 2009

Here is the update. I went out a few days ago and started the tractor then kept the carb warm with a hair dryer. It didn't die and after a sufficient warming period I jumped on the tractor and brushhogged half way around the field. I limped back in because after it sits for a minute or two it would thaw and restart. I have read that ethanol mixed in the gas can cause this problem, so I am going to try hooking up a small can to the fuel line with good gas and see what happens.

Anonymous-0 · Jul 14, 2009

If you kept engine running with a hair drier, this may well indicate your heat riser is not functioning. Weak spring, stuck shaft, burned out plate or just crudded up with carbon on inside passages surrounding intake manifold. Have not seen any problems with ethanol mix in these parts. If shutting down for a few minutes helps it is eiether freezing up inside or you don't have enough gas flow into carb, unless you have an igniton problem but does not sound that way to me. Up north here we have a lot of these kind of problems when using left over winter blend gasoline. Wouldn't know about your part of the country.

H. Springs · Jul 15, 2009

I don't know anything about heat risers. Is that attached to the coil spring on the manifold that seems to be connected to a butterfly type valve? If so, that could be part of the problem. I just bought the tractor in the March and the spring seemed really weak. In April, one day after brushhogging, I noticed the spring was gone entirely. I have manually turned the valve to both open and closed positions (although I'm not sure which is which) and it doesn't seem to make any difference. I can look at it further, it probably would like to be somewhere between open and closed. Thanks for your help.

Owen Aaland · Jul 15, 2009

(quoted from post at 11:53:43 07/12/09) The sweating is due to the vaporization process of the fuel and humidity in the air. As anything changes from liquid to a vapor it draws heat from somewhere so carb get cold and moisture condenses. May not be the pure scientific explanation of the process but that is the point of it anyway. Also, the better it vaporizes, like with a leaner mixture or better venturi system the more they sweat and if right outside air temp, freeze up. As far as running a minute, sounds like fuel supply into carb problem.

The fuel vaporization is only part of the reason that the carb gets cold. The other factor is air pressure. When air is compressed, heat is given off. This is the reason that air compressors get hot. The reverse is also true. When pressure is reduced the air gets colder and draws heat from whatever is around it. Moving air has less pressure than static air. The venturi causes the air to move faster, since it has to pass through a smaller opening, and is used to drop the pressure in the carb in the area of the fuel nozzle. The atmospheric pressure on the fuel in the carb bowl is then more than the pressure at the venturi which pushes fuel out the nozzle. This drop in pressure in the venturi also draws heat from the surrounding carb. Under the right conditions this can cause ice to form on the nozzle and restrict the fuel flow.

Sweaty Carb

H. Springs

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Allan in NE

Well-known Member

Red Mist

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Jeff Z.

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TomH in PA

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old

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Anonymous-0

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H. Springs

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Anonymous-0

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H. Springs

New User

Owen Aaland

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