Finn wrote:
Can anybody point me to an authoritative source (other than Tracy)
that explains why constant velocity carbs are not subject to icing?

I'm certainly no authority on engines or carbs, but I've never had an icing
problem. Constant velocity means no pressure drop, no pressure drop  means
no air temperature drop and no moisture condensed out, therefore, no ice.
Bob Moore

Blake Mantel wrote:

Sorry, to burst the bubble but CV & VV (variable venturi) carbs are susceptible to
carb ice. Though to a much lesser degree than normal ones. FI's can also form ice
around their throttles as well.

Remember that there is a an increase in velocity of air as it's pressure drops
across any given distance. (if it is idling it would be in the area of what... 20"
or more of mercury pressure drop from the outside air pressure to the cylinder
inlet). Remember there are throttle plates downstream from the slider as well.

I have had one (and only one) strange occurrence with my motorcycle on a very warm
and muggy winter day (visible moisture and 35-40'F temps) after I started my bike
(stored in unheated area) and had done some part throttle operation (old people
driving ahead!). Bike then started running rough and RPM's would not return down
to idle speed with throttle released. Killed the engine, pulled over and attempted
a diagnosis (by this time the heat from the engine was warming the carbs, finally)
and a few minutes later it was gone, completely.

Now this is one incident in years of driving, but is it enough to bet your life
on? I'd say no, at least if you fly in New England. But if you live in AZ or CA it
might never come up.....

Blake

Ice happens out here too. We have mountains. I took off once
at about dawn and experienced icing in my 182.

Paul Lamar
 
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