Webers

[911split]

What are the differences between Weber 40mm 3C-1 IDA, IDS, and IDT carbs? I'm looking to add Webers to a 3.0SC engine and like the look of the vintage Webers.

I've heard that PMO's may be superior, but what about among early Webers? Is there a preferred carb? And, can the early Webers actually be updated to perform identical to the PMO's?

Thank you,
John

[Wayne 962]

Some of the early Webers had an extra enrichment circuit, hence the difference between the model numbers. In general, the most commonly used ones are the IDAs...

-Wayne

[911pcars]

Here's what little I know about the differences:

IDAs - most common

IDS - used on early S engines. They have a high speed enrichment circuit that no other triple throat has. Some say this circuit is not needed and will actually shut it off.

IDT - used on my '69 engine, I noticed a different profile on the idle mixture screws. Less slope than IDA mixture screws. The effect is less idle mixture adjustment per revolution of the screw (emission-related). You can change these for IDA screws.

There are tall secondary venturis available, but don't think they were offered on a stock Weber.

Other than that, I think they are all the same save for the default venturi and jet sizes provided by the factory. Not sure about the other versions on the label in the pic.



Sherwood

[911split]

Thanks for the info guys.

[Grady Clay]

Guys,

Another subtle difference is the size and location of the “transfer ports” in the side of the body next to the butterfly. This affected the transition from idle circuit to the main mixture circuit and had a large effect on the “just off idle” performance.

Best,
Grady

[911pcars]

Grady,
Do you know which one had what?

Sherwood