Weber 40IDA3C Performance Modifications

Scheduling notice:

Please review Notice regarding scheduling of new projects.

Throttle Bore Modification

Throttle bore enlarged to 44mm from 40mm.  You can see how a 40mm throttle valve looks in the new bore.

Convert your 40mm throttle housings to provide improved airflow for your modified engine.  See Throttle Body and Main Venturi Sizing for technical discussion regarding bore diameter selection to match your engine's performance potential.  Conversion service includes:

  • Progression circuit modification appropriate for each bore diameter selected
    • Progression circuit designs for 43mm and larger throttle bore diameters are based upon the IDA progression pattern but tailored for each throttle bore diameter
    • Progression circuit configuration is not changed for 42mm throttle bores, this modification is offered separately
  • Tune-able idle air correction jets installed for 43mm and larger throttle bore diameters
  • Throttle shafts modified for larger diameter throttle plates
  • Available throttle bore conversions:
    • 40mm to 42mm @ $150
      • Progression port configuration of supplied carburetors is unchanged
      • Main venturis machined for correct taper from waist to exit diameter
    • 40mm to 43mm @ $350
      • IDA progression port configuration tailored for 43mm throttle bore diameter
      • Main venturis machined for correct taper from waist to exit diameter
      • Tune-able Idle Air Correction Jet Modification included
    • 40mm to 44mm @ $375
      • IDA progression port configuration tailored for 44mm throttle bore diameter
      • Main venturis machined for correct taper from waist to exit diameter
      • Tune-able Idle Air Correction Jet Modification included
    • 40mm to 46mm @ $400
      • IDA progression port configuration tailored for 46mm throttle bore diameter
      • Grub screws modified for retention of main venturis
      • Tune-able Idle Air Correction Jet Modification included

Throttle bore Modification is offered as an optional addition for either of the basic services offered (Re-Manufacturing or Restoration).

IDTP to IDA conversion @ $350

Weber IDTP progression circuit design.  Note diameter of holes and vertical spacing compared with that of the IDA.

Convert your Weber with IDTP progression circuit configuration to IDA configuration.  The IDTP version of the Weber carburetors are designed for use with 27mm main venturis and camshafts developed for the 2.0 911T of 1969 and for the 914/6.  When main venturis larger than 30mm are installed for larger displacement or higher performance engines, the progression circuit of the IDTP will deliver a lean transition in the 3000 to 3500 RPM region of operation.  The progression circuit configuration of the IDA does not suffer such a transition issue, which is why they remain the most desirable type of triple throat Weber for engines with more performance potential than that of a 2.0 liter 911T.

Weber IDA progression circuit design which is better suited for engines with large main venturis and camshafts designed for performance.

The conversion from IDTP to IDA progression is offered for either of the basic services offered (Re-Manufacturing or Restoration). Included with this modification is the installation of Tune-able idle air correction jets.  This conversion modification is offered only for 40mm and 42mm throttle bore diameters, larger throttle bore diameters include the IDA progression pattern as standard.

 

 

 

 

 

 

 

Tune-able idle air correction jet modification @ $125

Idle air correction jet is seen near the stud, there are three per throttle body.

This modification provides the tuner with adjustability of the idle/progression circuit beyond what may be achieved with simple idle jet changes.  The idle air correction jet in OEM Webers is a fixed-size orifice with diameters ranging from 0.80mm through 1.40mm depending upon application.  The ability to change the diameter of the idle air correction jet allows tailoring the fuel mixture characteristics of the transition portion of the idle/progression circuit.  When combined with idle jet size selection and the selection of main jet, emulsion tube and air correction jet for the main circuit the tuner achieves complete control of the fuel delivery curve.

Installation includes three sets of Idle Air Correction Jets and installation hex wrench.

  • Tune-able idle air correction jet modification - $125
  • Extra sets of air correction jets - $25/set of six

 

 

Install fuel well baffle plates @ $150/set

Baffle plate installed over main jet carriers after the fuel pick-up points have been milled  closer to the floor of the float bowl.  Two baffle plates are required per throttle body.

Classic modification to provide constant fuel delivery for road race applications when cornering loads approach 1G or more. 

 

 

 

 

 

 

 

 

 

Performance Profile for throttle shafts @ $125/set

The Performance Profile service option reduces the cross-section thickness of your throttle shafts which decreases blockage when throttles are wide-open compared to standard shafts.  Larger diameter throttle bores allow for more air flow than smaller bore diameters at the expense of decreased throttle response and delayed main circuit initiation.  Selection of a smaller throttle bore diameter for use with Performance Profile throttle shafts will provide the full throttle power of a larger diameter throttle bore without the expense or performance compromises of a larger bore diameter.  The Performance Profile is machined on your throttle shafts.

  • 40mm Webers with Performance Profile shafts flow like 41.5mm bores using standard 8mm shafts @ wide-open-throttle; an increase in flow area of approximately 10%
  • 42mm Webers with Performance Profile shafts flow like 43.5mm bores using standard 8mm shafts @ wide-open-throttle; an increase in flow area of approximately 10%
  • 43mm Webers with Performance Profile shafts flow like 44.5mm bores using standard 8mm shafts @ wide-open-throttle; an increase in flow area of approximately 10%
  • 44mm Webers with Performance Profile shafts flow like 45.5mm bores using standard 8mm shafts @ wide-open-throttle; an increase in flow area of approximately 10%
  • 46mm Webers with Performance Profile shafts flow like 47.5mm bores using standard 8mm shafts @ wide-open-throttle; an increase in flow area of approximately 10%