Finally got my twin carbs on and working well (36 IDF on 1600tp motor). I am happy with the way they are running, and can notice a fair bit more power.
However, especially when cold or idling they make some popping/sucking little noises - what could this be?
Also when starting cold the engine now needs a bit of warming up before it will idle without cutting out.

Any suggestions anyone?

i got twins on my dub to and it takes a bit longer to warm up, but its worth it to get more power out of the car

That popping noise is it is lean.

IF it goes away within a minnute i wouldnt worry TOO much. It will happen when it is cold and first off.

Are you DEFINITELY at best lean mixture. ie is the mixture screw at the SWEET spot????

You MAY want to try going up a size on the idles.

Any idae what size you have now???

Im not too sure about IDF's but on IDA's some popping at idle on cold starts is usually a good sign that its jetted about right.

blocked pilot jet.

also check your inlet gaskets, could be sucking air .

This will cause popping (to much air), and will affect idle when cold. Once the engine warms up and the manifolds/gaskets expand from the heat the problem will then usually go away/decrease. If this is the case then retighten or replace the gaskets . Did you use new gaskets ?