Frosted Carb

[BigE]

Hey guys. I went out to take my 1988 Argo for a ride last night, and when I went to throttle it, it just bogged, it didn't have enough power to turn the darn thing. It has the 16 horse B&S.
It idles good, you can turn the idle mixture screw, but nothing happens either way. while adjusting the idle I noticed the bottom of the carb frosting up. Whats with that?

[KrS14]

Could you possibly of had water in your gas, or fuel line, and it froze overnight when it was -0? Only thing i can think of.

[Mike]

That is due to Bernoulli's principle from the narrow venturi of the carburetor. When the throat gets narrow the air is accelerated. This increase in speed is accompanied by a decrease in pressure (that is Bernoulli's principle) and this decrease of pressure is what draws the fuel into the airstream and atomizes it. However with this increase in speed, decrease in pressure, and atomization also causes a temperature difference. In some carbs the temperature decrease at the venturi can be as much as 38 degrees F less than the outside air temperature. So even if the temperature outside is 70 degrees F the temperature at the venturi can be right at freezing.

Combine this temperature difference with either visible moisture or high humidity in the air and this can cause ice to form at and around the venturi. Typically this will reduce power a little which isn't a big deal but there are a couple of engines that it really effects. Corvairs were notorious for having a huge loss of power from carb icing and all of the aviators out there know the theory well because carb icing in an airplane can of course be detrimental. Most (if not all) airplanes with carburetors even have a method to direct heat from the manifold back into the carb to eliminate any ice.

That was way more than you probably wanted to know but I'm going to renew my pilot's license soon and it's fresh in my mind.

[dezi]

I think my brain just Farted. I feel a lot dumber now thanks to Mike.....

[KrS14]

+1 Mike!