What are the differences in webers?

[911Bus]

Can someone fill me in on what the differences are in the 40mm weber carbs? 40ida3c, IDT and others. Whats better and why?
Thanks.

[jluetjen]

The IDS's have some extra features (a high speed enrichment circuit) to enrichen the mixture at max rev's. In hindsight, with modern fuel and some jetting changes I've heard that those features aren't really a big deal.

I'm not sure of the differences between the IDA's and IDT's except that the IDT's were spec'd for the 911T's. The differences may have just been in the jetting and venturi size initially installed by Weber.