My carburetor story

[JPM]

Webers can be modified

A bit of background. Starting from a stock 69 911T, I decided to upgrade to a higher powered 2.4S engine with E-cams based on reading research and forum comments. Since I had carbs on the original engine, I intended to use them making appropriate jetting changes following a recommendation from PMO, I believe. Unfortunately, carburetor literature is scattered around and I had not read about the different versions of the 911 Webers.

My re-jetted Webers were performing okay but I wasn't sure I was getting the most out of them. I knew my carb version was IDTP but not much else until I came across a discussion of the merits of the other Weber versions, IDA, IDS, IDT, IDAP. This put me in touch with Paul Abbot of Performance Oriented, well known here, who informed me through his web site and correspondance on these differences.

I followed Paul's recommendations to add adjustable idle air jets and replace the throttle bushings with a kit you can do at home. You can make an IDTP more like the IDA which is the primary version recommended for higher displacement engines. The major difference remaining is in the progression circuit but you can live with that by adjusting the idle air jets. I am happy to say I have reached a much better performing carburetor as a result. For those interested in my jettings:

Old: 32mm Venturi, 135 Mains, 180 Air, 60 Idle, 140 Idle air(Fixed), F26 E-tubes
New:32mm Venturi, 125 Mains, 170 Air, 55 Idle, 100 Idle air(Adjustable), F3 E-tube

Adjustable air jet installed


Bushing replaced


I considered getting PMOs but its good to know you can get decent(and less expensive) results with a few mods to the IDTPs of which there are more around than other versions.

JP

[72911]

Great work. I love to hear about people solving their own issues.

[mb911]

Where did you get the bushings?

[Trackrash]

Not sure about Paul's bushing, but I replaced the plastic original with one made out of sheet brass on my Webers. Worked fine for years.

[1QuickS]

I've made brass sheet bushings as well to same effect. The ones for JPM were turned from steel reinforced, SAE 863 sintered bronze bearing stock.

[JPM]

Actually, Gordon, the challenge was finding the plastic one it is so thin. If Paul hadn't insisted I would have given up! One side was looser than the other and easier to see. Resizing the progression holes like you did was a nice idea.

JP

[Jack Stands]

I think Paul knows more about these carbs than Weber does at this point. Enthusiasts should be very happy that he and Rich Paar (PMO) are around.

[mb911]

Can you explain the adjustable air correction?

[1QuickS]

Idle/progression circuit & main circuit each use air jets to emulsify the fuel drawn into the engine. The air jets for the main circuit may be changed to adjust this emulsification but stock Webers for the 911 engines have a fixed size air correction jet for the idle/progression circuit. I developed a kit to allow users to select idle air correction jets to help tailor fuel emulsification during idle/progression/transition.