Re: [T3] ducting more air into the engine compartment for 42dcnf carbs

["Steven Ayres" <comwest@att.net>]

DavidG=> Fabricate sealed ducts ... Would you be willing to explain ...

Consider the stock dual-carb arrangement, as illustrated in your carbed-Type 3 manual. You have an intake pocket in the body (on the side in fasties and squares, under the rear window in notches or under the engine lid on Ghias). This handles both engine cooling air and carb air. There's a duct from the body to the air cleaner, and the air cleaner bridges the carbs, all sealed away from the compartment air (niggle: there's a switchable port for compartment air in the winter to help prevent icing). You'll want to build a custom duct arrangement that carries air from the body pocket to the carbs, incorporating air filtration because you don't want to screw up your no doubt expensive custom motor with dirty air. 

=> I live 110 deg. weather.

I guarantee your intake air is too hot. This may not be the whole problem, as Jim intimates, but it's part of the problem at least. It's a common one for aftermarket carb setups, which are designed for Types 1 and 2, not Type 3. Overfueling is also a very common and subtle problem, even with stock carbs.

=> vapor lock after I turn it off, sometimes boiling in carb floats

Boiling fuel indicates that too much heat is getting to the carbs from the heads. VW handled this using thick fiber insulators between the carbs and the intake manifolds. It works. You may be running too hot in general, and with a big motor this is always a challenge, but if your carbs are not insulated they're likely to boil even at in-spec engine temps. 

Steven Ayres, Prescott AZ
'66 Big Ghia

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