Weber 40 ids

[jdj123]

I have a set of Weber 40 IDS that do not have the enrichment pipes for high speed(RPM) and would like to modify them in order to install those tubes(pipes?)
Do you know if some IDS were delivered by Porsche factory without those enrichment tubes(pipes?) or if all IDS had always those improvements for high RPM.
I read in the Porsche technical book at chapter "fuel delivery" that only the last engines 1968 911 S( 2.0L) where delivered with the WEBER IDS modified with the enrichment tubes(pipes) and that before engine number 4080773 all IDS did not have those specific enrichment tubes.
is it true, could you please confirm.
thank you all for your help.
Cheers, JD.

[haycait911]

I thought all IDS had the tubes. do your carbs have the holes to mount the tubes? can you post a pic? if you have the holes maybe they were taken off at some point. here's a pic of IDA vs. IDS.

[chris_seven]

I have a set from a 1966 built 911 and they have booster jets.

[docrodg]

40IDS carbs were only made for MY67-68 911S. A set from a 66 would not be IDS but IDA. The first 911S models got carbs marked 40IDA3C1S and 40IDA3CS as they were simply IDA's set up and tuned differently for the S engine. The IDS was added MY67. They were changed in 1968 to add the enrichment jet to prevent detonation at high RPM. Whether that change was beginning or mid-year I am not sure but the jet was added in MY68.

Wish I had the originals from my engine, but they were removed for a set of IDAs a long time ago by PO during a smog check. The guy doing the check couldn't get the car to pass and swapped them out for IDAs. Whether that was really needed or not is something I question, given the value of IDS carbs.

Long story short... IDS are correct, but the only real difference is in the enrichment circuit (functionally) for certain models and this enrichment is not necessary for occasional short bursts at high RPM. If you have the circuit and you have a smog check requirement that the enrichment is playing havoc with I would just remove plug the feed circuit to the nozzle.

PMO has a nice bit of info on their site about the external differences (fuel passages) between the two carbs.

[edmayo]

Here is some information from a previous post that might answer your questions. Do a search for Weber 40 IDS as there are other posts that list engine numbers also." Hard to find indeed, I have no spares. OK to run without, definitely. They have exactly the same progression circuit and idle air bleeds of the IDAs and the remainder of the bits are interchangeable. It would be good to plug the hole in the top of the main throttle body that feeds them. The earliest 2.0 911S engines used IDA carbs that were stamped with an "S" to identify their unique jetting which was: 32mm venturis, 135 mains, 170 air correction jets, F26 emulsion tubes and 55 idle jets. The IDS carbs were the same except they used 125 mains, 185 air corrections and F3 E-tubes.

I have a customer who vintage races a 914/6 with dyno work showing there to be an advantage in high RPM HP but street applications don't need them in my opinion. Best guess is they were used to help enrich during sustained high speed cruising (Autobahn) to avoid piston melting.

Note that they were not offered for after market sales by Weber after the carburetted 911Ss were no longer in production. "

[Silverbullit]

The earliest 2.0 911S engines used IDA carbs that were stamped with an "S" to identify their unique jetting which was: 32mm venturis, 135 mains, 170 air correction jets, F26 emulsion tubes and 55 idle jets. "

I can confirm this as that is what is on 305811S. Brian

[jdj123]

Thanks to You Guys, for those clear technical explanations.
this forum always provides the right answers to any questions.
regards,
JD

[Neil '67 911S]

The earliest 2.0 911S engines used IDA carbs that were stamped with an "S" to identify their unique jetting "

Hi Ed,

Where on the carb body is the "S" stamp? Ol' Ivory is a mid-Sept. 1966 911S. It does not have IDS carbs.

Thanks!

[1QuickS]

Here is a picture of a "S" stamped IDA carb; this is from a 1967 911S per my customer. By the way; haycait911 provided a photo of an early IDA throttle body (top) with the IDS version, later IDA bodies were cast with identical features which would allow converting them to IDS specifications and therefore have the holes shown in the picture of the lower throttle body (IDS.) The difference is that the IDS bodies would have M4 tapped holes in three of the four holes closest to the exterior wall of the throttle body and the fuel galleries adjacent to those tapped holes would be drilled down to the horizontal runs (on the exterior of the bodies) which are drilled through to the fuel wells and then lead plugs are used to close the exterior ends of the horizontal runs.

Even the USA made "Weber" throttle bodies have the provisions for IDS fuel galleries for the high speed enrichment tubes. I assume that the early IDA bodies were cast in a production run and when the need for high speed enrichment was discovered then the next batch of bodies incorporated the added fuel gallery features so standard IDA or IDS bodies could be produced.

[Neil '67 911S]

Hi Paul,

How cool is that! I was reasonably sure that Ol' Ivory sports its original carbs and your photo confirms it.

Thanks for the post!