Weber 40 Carbs on 911 S Engine

thdbeat1 · 08:10 PM

I have a freshly rebuild 911S Engine From 1967. This has been Rebuilt with 2.2L P&C's. I am wondering about the best configuration for Webers on this engine.
Please provide any thought as I would appreciate it. My Current Webers 40's are IDTP.

Thank you for your help!
Erik Black

1QuickS · 05-20-2010, 10:19 AM

32mm venturis, 135 mains, 55 idles, F3 emulsion tubes, 180 air correction jets. If you want to rev it up a bit higher for your power then 34mm venturis and 145 mains keeping the other bits the same.

The IDTP carbs do have a leaner progression circuit than the IDA/IDS/IDAP carbs and the air correction jet in the body (currently a 1.40mm) should be modified to be 1.10mm to help overcome a 3k RPM flat spot. Contact me about this if interested in the modification. The pictures show IDA vs IDTP progression circuit holes and the modified air correction jet.

Picture of IDA/IDS/IDAP progression circuit holes

Picture of IDTP progression circuit holes

Picture showing modified progression circuit air correction jets

Paul Abbott
www.PerformanceOriented.com

Peter Zimmermann · 05-20-2010, 10:46 AM

Unfortunately, one of the keys to top end performance with the early, small displacement, S motors is that only the "S" Webers (IDS) were fitted with high speed enrichment. You will be somewhat forced to make up for those with jetting adjustments. I prefer a slightly more conservative approach than the one listed in the above post (although it's OK); and have had success with 32mm venturis, 125 mains, and then play with air correction jets between 170 and 185.

Another mixture-related issue is the injection quantity; .8/stroke for the IDS, and .5/stroke for the IDT.

You want to make acceleration runs after the engine is broken in, followed by spark plug reads, to make sure that the combustion chambers are getting what they need. Because of deck height choice, accuracy of cam timing, ignition distributor advance, heads/ports/valve sizes, etc., every engine will be just a little bit different, so be careful with initial jet combinations, as well as follow up adjustments.

kenikh · 05-21-2010, 11:09 AM

High speed enrichment in the IDS was in my experience snake oil. I have heard the same from several wrenches who were working on these cars professionally when new. It was supposedly to richen the mixture on top end to address detonation issues. Have run both IDS and IDA, the theory never transalted into reality.

I've run IDSs on my '69S and IDAs on the '69S and '66N w/ DC30 cams, both beyond 7200 RPM for extended periods. The IDAs run great.

thdbeat1 · 05-22-2010, 09:55 AM

I appreciate all of the pictures and details that have been sent !

So I went to get my other Set of Weber Carbs only to find that I accidentally Sold them with another engine it was supposed to include the Zeniths I had and I gave them a bonus incorrect box...

Anyway... I have Purchased a Set Of 40 IDAs and Now Will Be using them instead.
So I will Now be using the IDA Carbs as these I am left with are for My 914-6 Project and are the correct originals .

The Dissasembly Process of my 914-6 Carbs Damaged a couple of bits that were $#@! near welded in and these will now require extraction. The Weber Diagram unfortunately shows the other side of the carb and not the side I need to determine replacement parts. Can someone please identify the proper part numbers for the replacement parts where the screw based still remain within the carb and need to be extracted?

Also,
So with the IDA I may need to contract a modification from one of you to provide the optimum performance with the 2.2L 1967 S Engine and the Weber 40 IDA Carbs. Please let me know what may be required and I would welcome some ideas as to the cost for upgrade machining and cost for replacement parts for correct jets etc.
Thank you
Erik Black

0396 · 05-23-2010, 06:28 AM

To answer your above question.. Paul's your man :
Paul Abbott
Performance Oriented: repair, restoration and modification of Weber carburetors

0396 · 05-23-2010, 06:33 AM

To answer your above question.. Paul's your man :
Paul Abbott
Performance Oriented: repair, restoration and modification of Weber carburetors

1QuickS · 05-24-2010, 10:51 AM

Those are the main jet holders (Item #29) and typically are over torqued during assembly. They are brass, hollow and have cross drilled holes so they have lots of stress riser issues. These need to be removed using a very carefully set-up drilling process, best left to someone that has experience in doing this as a mistake in centering up WILL run the drill into the threads in the Weber body and WILL seriously compromise the seal established by the threaded interface of these items.