I have just got a 1600 twin port for my '68 beetle from a friend who had it in his shed for about 10 years. I'm looking at the manifold that the carby sits on and there is a tube welded on the left side about 1 cm thick but I don't know what it should connect to. I found a picture of this model engine with the tube and it connects to a device bolted in the top left of the engine bay.
Is this some kind of emission device? Do I need it or can I plug up the tube? Any advise on what I should do would be great.

If it's original, there should be a tube that runs from the RH exhaust port across the manifold and connects to the muffler.
This sends some exhaust gas along the inlet manifold to heat it up.
It's for better cold weather running. You can live without it if your in a warmer climate, but make sure the tappings into the exhaust are plugged if you don't use it!!
:thumb

Sounds like its a Kombi engine, and that might be the fitting for the Vacuume brakes, is it just below the carb on the LH side?

It's for vacuum brakes on a Kombi, block it up :thumb