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Re: general carb icing question

To: Phil Bates <>,
Subject: Re: general carb icing question
From: Hans Duinhoven <>
Date: Sat, 23 Dec 2006 14:13:17 +0100
Icing on carbs comes from the fact, that for evaporating of the fuel inside 
the carb heat is withdrawn from the carb housing. On top of this when in 
winter the weather is damp, the outside of the carb will reach temperatures 
below freezing point, because of the heat is making a very cold carb 
casting. The dampness will condense on the carb housing and form an icy 
layer. This event even may occur when the normal air temperatures are quite 
above the freezing point.

You can try to prevent this happening by having the carbs protected in 
winter time by getting just a little air flowing around the carbs, but 
beware it is important not to obstruct the air inlet of the carbs.

Do not forget to remove this protection in summertime, as you may end up 
with the vapour lock event caused by too hot carbs.



1971 BGT

P.S. Merry Christmas & happe new year to all listers!

----- Original Message ----- 
From: "Phil Bates" <>
To: <>
Sent: Friday, December 22, 2006 4:36 PM
Subject: general carb icing question

> This is not an MG question, but I figured someone like Barney may have
> background knowledge on this.  I have a car with downdraft IDA weber carbs
> - one per cylinder - no chokes.  It's a little tough to start cold, but it
> works.  Anyhow, twice, my car has started to run crappy in the snow.  When
> I stopped driving I opened up the engine compartment to see that there was
> frost on the outside of carbs.  The first time it was one carb.  Today it
> was 3 of the 6 showing frost on the outside of the carb.  I haven't had
> the opportunity to look inside, but suspect its icing in there too.  What
> I don't know is this - what exactly causes icing??  I know it's the
> venturi effect, evaporation, and moisture - but is there a lean or rich
> condition that also increases the likelyhood of icing??  What is the
> effect of carb icing - do I end up with a chunk of Ice going in my
> intake?? Or maybe a jet blanking off due to ice and then a lean mixture??
> Phil Bates

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