I'm in the middle of learning about weber carbs so I can tune mine properly. When I was checking the model numbers I noticed they're slightly different - I have one 40IDS3C1 and one 40IDA3PC.

From what I can find, the first came off a 67-68 911S and the second is off a 68 911 or 911L.

Other than the different model designation codes are these essentially the same carb? I'm guessing they are, but would have originally come with different jets to match the different performing 2 liter engines.

One thing I might do is to go on the Early S Registry and place an ad explaining you have one IDS weber and you would be willing to trade it for a perfect (and matching) condition IDA.

http://www.performanceoriented.com/weber-d...n-variations-1/

I have a spare Ida. But run ids carbs. I would trade you and pay the difference

The ids carbs have a high rpm enrichment circuit to fatten the mixture above 6000rpm

Thanks Mark.

Brant, thanks for the info. Let me educate myself a little more first - I'm new to carbs and want to understand what I have and how it relates to the engine in my car before I make any decisions. If I do decide to swap it out you'll be first on the list.

Yes you are correct. The 40IDS3C and 3C1 (one is left side and one is right side) are from the '67S (USA), '68S (Europe). It's essentially a standard 40IDA but has an enrichment circuit on the top. Look down the intake, see a little tube pointing down to the venturi? That's what makes it different from the IDA.

I had a '67S once and that's where I figured that out.

most of the time when these carbs are used on other motor applications, the enrichment tube is removed and plugged.

I had a supertec motor and henry had plugged all 6 of these enrichment circuits
they are usually plugged with a small allen head plug

when intact, there is (as described above( an enrichment circuit that sticks up above the air horn and looks like an upside down "j" or a miniature kitchen faucet

it pulls fuel from the bowl and once primed the vacuum signal from high rpm pulls fuel into the air stream of combustion,

thus the signal has to be strong enough that it only adds extra fuel at high rpm
they do prime and with a wide band AFR you can see that no extra fuel is added the first 2 runs to redline, but once primed they add extra fuel

probably a better idea for street than race, but my car is set up and has always ran them, so thus my interest

due to this extra fuel, the jetting for the rest of the carb has to be adjusted to compensate

but it does allow you to run a more lean mid range and still have adequate fuel for very high rpm

with the circuit plugged (most likely in your case) its just a standard carb in application.

note you can not run the enrichment tubes with tall aux 2ndary venturi's
and also note that there are different jets available for the enrichment tubes, so that the amount of fuel added could be metered or adjusted.

once the tubes are removed, they are very hard to find used
took me a year to fine the set I have now.
although supertec must have a box of them somewhere....

On this page IDS carbs are in the level 2 and 3 pic's.
IDS carbs has the little kitchen faucet looking tubes, they are what Brant is talking about.


http://www.performanceoriented.com/weber-40ida3c/

Thanks guys! A wealth of information, as usual. I'm guessing the IDS has had the enrichment circuit plugged - wouldn't it effect performance if the two were different? I'll take a closer look this afternoon and report back on what I find.

Looked inside the webers today. No squirters in the IDS, in fact the pair look exactly the same. These two shots are of the IDS:





And here's the IDA: