Weber carburetor dating and history of changes

[1968DT]

Originally Posted by 1QuickS

I believe those are from a Sportomatic installation and for a 1968 year model. The manifolds for a 911S will have exit port diameters of nearly 36mm while the other ones are 32mm. All die cast manifolds share the same casting part numbers and all have date codes on them. I attach some info which is helpful:

Intake manifolds info
I have reviewed a selection of OEM intake manifolds to help answer some questions regarding individual variations between the years from early 1966 through 1970. I have a sample of manifolds for each of these years which I reviewed so I feel confident the gamut of variations is pretty well covered. Each of the manifolds has a date of production except for the manifold I believe to be the earliest which is sand cast and doesn't have a date.

Info presented in no particular order:
• I have one set of sand cast manifolds without mfg date
• All other manifolds are die cast
• both types of 1966 manifolds (sand cast and die cast) have an oblong, internal cross-section in the outer runners
• 1967 through 1970 manifolds all have conical bores
• my 911S manifolds (mfg 1966 and 1967) have a 35mm bore in the middle and has oblong outer runners
• 1966 manifolds (sand cast and die cast) have 34mm bores
• 1967 through 1969 manifolds have 32mm bores; 1970 bore measured 31.5mm
• starting in 1967, reinforcing ribs extend from the bottom flange up the exterior of the runners; 1968 and later manifolds have larger and longer reinforcing ribs
• starting in 1968 the lug for the 8mm bell crank has an added reinforcing web
• sand cast manifold part number is: 901.108.321.01
• die cast, 1966, 911S manifold has part number: 901.108.321.0R
• die cast, 1966, Normal 911 manifold has part number: 901.108.321.1R
• 1967 and later have ports for Sportomatic and/or other vacuum accessories
• The two measured manifolds (sand cast and die cast versions) are magnesium. I measured volumes and weights (volume by water displacement method a la Archimedes), I then corrected for steel studs that were installed. My calculated densities matched the published density for Mg to the second significant number (density for aluminum is 56% greater than Mg and well outside my tolerance band); I conclude that all I have are magnesium.
• My inventory included manifolds with dates from 1966 through 1970 without interstitials.

Remember that the manifolds for Solex carbs were magnesium so I expect Porsche would keep the material for Weber carbs. I assume the sand cast manifold was for the first few Weber 911s which began to appear in Feb 1966 with engine #907001 as the Solex carbs were phased out.

Ignore black finish applied to top three manifolds. Earlier manifolds may have been coated with a protective finish while later ones were painted with a VERY tough, gloss black coating (polyurethane?)

Also, I expect there are versions with date codes that would fit into the above collection such as those manifolds made in 1967 but do not have the changes that the manifold I have that show for 1967, in other words I bet there are 1967 manifolds that physically match the die cast 1966 manifold.

Thanks for the info, they are 901.108.321.1R w/ a 67 casting date with vacuum to distributor. Looks like 31 to 32 bore.

Well the hunt continues....

[Carrera C4]

Hi, long time since no one talk.... well I would like to refloating this topyc, becuse I have just purchased a 911 s engine from 1967 with their carburetors (it is a totally barn find!!!) in fact I was looking for some pieces for other of my Porches when I found it. My question is... mine are 40 ISD 8C/9C serial number 1242, why 8C and 9C in instead of 3C??

Thanks a lot.

[Quickstep192]

What is the second picture of in this post? I don’t recognize it and the curiosity is killing me.

Originally Posted by RatBox

Here , I dug through my photo's , as I knew I had one carb number photo which I had noted which car it was from.

This carb is from 1967 911S no. 306615 (I don't have a photo saved of the COA. But I saw it , when I saved these photo's. And the date noted (if they transcribed the correct one) was Nov. 3, 1966. It was a U.S written COA . If you zoom in on the number , it is 40IDS3C1 no. 1491. This car was said to have been very original before restored . I believe when numbers start being posted tied to car serial number . Only carbs from cars which people have a good inkling that the carbs have a good chance of being original to that chassis , should be posted. And I think the carb numbers are going to do a certain amount of jumping high & low , as the motor assemblers were not looking at the numbers. Just grabbing the proper type. That is why also , I believe (?) a 67/68 911S can originally come with a 40IDS3C1 , along side a 40IDS3C (that is after the point when 3C1's were introduced) . But there could be a (general) progression in numbers . It really depends on how many carbs of each type Weber shipped the factory at one time. Remember, I'm believing that EACH type, started with unit no. 1. So there would be a series of numbers starting with No. 1 for 40IDS3C's . Just as there would be for 40IDS3C1's :







I cannot be 100% certain. As I did not make a note, but I believe the motor number of this car was 960841. Maybe someone else saved a copy of the COA when this car was being marketed (or made a note of engine to car / davep ?).

[ecostellodo]

Looks like a headlight bucket to me. The number stamp should match other stamps on the body panels.

[angelny911]

Chime

[Carrera C4]

No answer, no theories? why 8C/9C instead of 3C????

Thanks a lot

[geoff_68s]

> No answer, no theories? why 8C/9C instead of 3C????

Can you post a photo? I suspect it might actually be 3C, notwithstanding some wear or casting marks or somesuch. Pretty sure that the '3C' in, for example, '40IDF3C' means "triple choke", (or, more likely, the Italian equivalent), which differentiates the 40IDF3C from the 40IDF, which is a very similar 2-barrel carbeurator.

[Carrera C4]

Of course.

And thanks a lot

[Carrera C4]

Big apologies for the delay and for misundertsnading! you were right after an accurate clean....is 3C

[Norm01]

Originally Posted by djpateman

Yes, a new little database started.

Can you post any database info?

[1QuickS]

Take a closer look. The picture shows driver's side carb. Top numbers should read: 40IDS3C1 and without spacing between them. The photo looks like 40IDS3C1 to my eye. The lower numbers are the serial number and look to be 1491.

That looks to be un-molested with OEM, tall nylock hex nuts and OEM safety wire on the grub screws securing the main venturis.

[rory gallagher]

Originally Posted by ecostellodo

Looks like a headlight bucket to me. The number stamp should match other stamps on the body panels.

Yes, headlight bucket.
Has the last three digits of the VIN which were typically on all removable
panels. Also note the 'S' below which the last character the VIN on S cars only

[fishfan009]

What were the numbers for the '72-'73 2.4L cars?

[75 911s]

Great thread.

Looking at the carbs I just bought, I would say they are from 1970 plus, would that be a fair assessment?

The thought crossed my mind of passing these on and buying PMO, but something about the vintage carbs is attractive. I love PMO and I do think they have a few superior design improvements, but looking in my bay, kind of cool to see a period correct part in there.

I was hoping to shed a little light on the history.This thread says my carbs are from around 1970, identified by the stamping 5H and 5J. Is this accurate? Thanks for any help.

I'll be installing these on my 75 911. It's a stock motor at the moment. I'll be rebuilding it in a few years and at that point, I'll probably go to a 2.7RS build.

They look pretty clean, but I want to rebuild them as I don't know the history and rather than put them on and trust them, I would like to go through them as it will ensure everything is up to snuff and I'll learn the ins and outs so I can have a better understanding when I tune them.









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[Targa68]

Must be very early