I've made a small high rise adaper for my Reliant engine .It , like even Beetlehirise standard manifold would be cold and even actually form ice. I wrapped mine in leather look , comfy feel bicycle handle bar tape and solved the problem.

 

That's a cracking idea thank you Kev, I have the same issue on my Ford sidevalve custom manifold, will try your approach.

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have you checked inside to see if there is any condensation? it's probably only on the outside and caused by the flow of cold/fast air fuel mixture going through the manifold. the same as the fittings on your oxy/acetylene regulators get condensation and frost on them when welding.
neil.

 

The condition you describe is due to thermodynamics that are induced by the vapourisation of fuel from liquid to gaseous state thats is exaggerated by the airflow through the manifold
Look up joule tomson effect on the net to understand this phenomenon. A heater matrix of some form is required overcome this and prevent freezing ( lpg systems do it all the time hence the use of a water heating jacket on the vapourising units).
We use jacketed pipes to overcome this when designing liquid-vapour ( pressure reduction) transition pipework.
The heater pipe you describe will need to wrap tightly to the manifold and then be insulated too.

 

Thanks for your input chaps, I once experienced extreme carb icing after I changed the carb and air cleaner on a Series 1 Landrover and it stopped dead cos the whole inside of the carb became blocked solid with ice!

I found this article which explains the condition in lay mans terms: https://www.hemmings.com/stories/article/carburetor-icing

 

You can buy an IMDU - an electric inlet manifold de-icing unit. Its a little jacket that fits around the manifold which is 12V. Lots of aircooled vw's have this issue

Mal