Cause of carburator icing

hydro70guy · Apr 12, 2018

On my hydro 70 gas, it has an updraft Marvel-Shrieber I just put an electronic ignition on it and took for a drive. Got it good and warmed up and back to shop and carb was iced up from about where venturi is and above. What causes this and is it a problem I need to address?

Thanks,
Joe

gene bender · Apr 12, 2018

air temp and RH carbs will do that and they have since they have been used.

Bob · Apr 12, 2018

Carb icing is a natural phenomenon of air and fuel expanding after passing through a venturi.

Your tractor would have a "heat riser valve" to deflect exhaust to heat the intake manifold above the carb (and to a degree the carb by convection) during warm up or at light loads.

SOME icing is "normal", if the heat riser is stuck in the "hot" position or the "valve" inside the manifold is missing or broken, it will be worse.

pete 23 · Apr 12, 2018

You hit the right air temperature and humidity. When fuel vaporizes in carb it take heat out of the air and if things are just right, the moisture in the air freezes. Now I know that is not the exact scientific explanation but it works for me.

Notice your manifold has a thermostatic spring loaded heat riser. That has a lot to do with the problem also because they have to be kept in good condition, and also, the internal heat stove in intake manifold gets all full of carbon.

Just shutting down for a little while , allow that ice to melt, start up again while still hot and it may not bother until next time.

Bob M · Apr 12, 2018

Same as the others have said! Icing occurs at temperatures between freezing and about 50 degF combined with high humidity.

Extended idling/light load operation causes the worst icing - avoid it if you can.

A properly operating manifold heat valve and avoiding idling after a cold start (put the tractor to work immediately) minimizes icing. If carb ice does cause problems, shut down the engine for a couple minutes and let manifold heat soak down to the carburetor to melt the ice.

ss55 · Apr 12, 2018

That is normal when humidity is high and the tractor is lightly loaded. If it bothers you you could install engine side covers to direct warm air from the radiator to flow around the carburetor (and hide the frost that does form from view).

hydro70guy · Apr 12, 2018

I was not bothered by it but was curious. Also found out what that small thermos coil on intake was, I have had the tractor since new and never knew or asked what it was for.

Thanks for response. I had a good day any time I learn something new, or that's what I tell my kids anyway.
Joe

Cause of carburator icing

hydro70guy

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gene bender

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Bob

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pete 23

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Bob M

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ss55

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hydro70guy

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