FAO Robby IMDU

One of the most common problems for beetles which retain the stock carb and inlet manifold set-up is manifold icing.
Has your bug run rough when cold, or cut out at idle until the engine has warmed up?
If it has, the problem could well be Manifold icing. The problem with
the stock manifold is that it is a long way from the carb to the
cylinder head (dual-carbed engines do not have this problem).
When the air/fuel mix from the carb reaches the base of the manifold,
just before it (the manifold) splits into two pipes (one to each
cylinder head)
it is at its coldest and this is where icing takes place. You can see
this in the form of condensation on the outside of the manifold)
VW themselves were dogged with this problem. The two smaller bore tubes
that run from either side of the exhaust to the base of the manifold are
heat-riser tubes designed to combat this problem. These are known as
'single hotspots'.
The factory tried again by giving later models 'Dual hotspots' - that is
- four small bore pipes (2 each side) from the manifold to the exhaust -
with little success.

One solution to this problem is an IMDU
This is a basically a small electrically heated blanket which wraps around your manifold to warm it up.
Price is about twenty pounds (sterling).