Tuneable High Speed Enrichment Tubes for 911S Webers

[1QuickS]

Not much call for this but interesting project: I have developed a kit to allow adjustment of the High Speed Enrichment Tubes as supplied with 40IDS3C Webers for the 1967/1968 model years. Picture shows the bottom of a modified HSET.

Only for those wanting all the tuning options:

[Mr9146]

What's the correlation between the threaded plug depth and the fuel flow? How well does it work?

[1QuickS]

Just a picture of a replaceable jet which is a set screw that has fuel metering hole drilled through its long axis. Picture was taken from my Installation Procedure to show finished installation depth; tap-drilling & tapping depth result in tapered internal threads that secure "jet" without it bottoming out.

I know that Ed Mayo increased the orifice of his HSE Tubes on his 2.0S from 50 to 70 with positive results. Otherwise an unknown entity for mixture control. I had a customer request them so I provided a kit to support his request. HSE Tubes were 50 for the 2.0S but I do know that larger sizes were offered, I have a set of 70s in-house at this time.

When I serviced Ed's Webers he requested that I solder the HSET orifices closed. He later opened them up to 50 and now to 70.

The High Speed Enrichment Tube is not unique to the triple Webers used on the 911S. The Solex carburetors routinely used them for enriching upper RPM operation while providing separation from midrange main jet & emulsion tube selection.

As an example of the benefit of the HSE Tubes I refer to OEM jetting differences for the first Webers (IDA (S)) for the first 911S models from August 1966 and the revised Webers (IDS) for those being delivered beginning in the November 1966 time frame. The IDA(S) Webers did not have a HSE Tube so the main jet, emulsion tube & main air correction jet were somewhat richer than the IDS Webers with HSE Tubes. It is my understanding that the high dome of the early 911S pistons lead to detonation at peak RPM & loading so a rich mixture was adopted to overcome this issue. Since a rich mixture is not optimum for performance across midrange the HSE Tubes were adopted to allow a better midrange jetting and keep rich mixture during high RPM operation.

IDA(S) jetting:

• 135 main jets
• F26 emulsion tubes
• 170 main air correction jets

IDS jetting:

• 125 main jets (leaner than 135 main jets; affects entire main circuit mixture)
• F3 emulsion tubes (very similar to F26 tubes in hole spacing & diameters but the pattern location along the length of the tube provides an earlier activation of main circuit with a little extra leaning action at upper midrange)
• 185 main air correction jets (leans out mixture at high RPM compared to 170 correction jets)