Volkswagen Weber IDF




Volkswagen Weber IDF



The Weber IDF has been considered the ultimate carburetor for off road use.  But now that they are no longer being made and with the increased popularity and adjustability of fuel injection, the carburetors may become a thing of the past in the years to come.



Weber IDF Set Up

From the factory, these are not ready to be run in a VW.


The first thing you will need to do is inspect the carb and do a good cleaning.  You will need to set your Floats.


For dual carburetor applications, the chokes will need to be replaced with a block off plate and two smaller screws.  The reason behind this is that they like to collect dirt and will more than likely contact the stock fan shroud.  They are generally only needed for sub zero temperatures.




Adjust the Idle-Air Screw so that the butterfly valve and the side of the carburetor barrel wall on the side of the Idle-Air Screw is 0.004 inches.  An appropriate size feeler gage should slide out of this opening with just a bit of resistance.  This will most likely give you a high idle, but will help you get to a good starting point for your dual setup.



Gently turn the Idle Mixture Screws clockwise until they bottom out.  Do not force them.  Then unscrew them counterclockwise 3 turns each.


Gently turn the Air-Bypass Screws clockwise until they bottom out.  Do not force them.  Then unscrew them counterclockwise a half turn each.




If you want the fuel lines on the same side (front or back), you will want to make sure that the Fuel Inlet Pipes are where you want them.


Depending on your setup, it may be easier to hook up the fuel lines on the carbs before you install these in your VW.


Now install the carb on the intake manifold and the manifold on the heads.  Note that the cylinder covers often need to be modified to allow these manifolds to fit.  Paper gaskets work better than the OEM stamped steel gaskets and should be used on the mating surfaces between the carb and manifold and the manifold and the heads.


Install the air filter bases and linkage.  Do not connect the linkage to the throttle lever just yet.


Get your fuel lines hooked up and get everything read to fire up your engine.




After a warm up, use an airflow meter to measure the airflow over the barrel nearest the idle air speed screw of each carburetor.  Now adjust the idle speed screw until both carburetors match.  This is called carburetor synchronization and is vital for optimal performance.


Adjust the your linkage so that it connects to the throttle levers without moving them.




Now it's time for the real carb tuning.  Start with the barrel over cylinder #3.  Turn the Mixture Screw in clockwise until the engine misses (bogs, snapping, popping, etc).  When you get to this point that cylinder is too lean.  If you can't get to that point then you may have a vacuum leak somewhere, a clogged jet or a dead spark plug.  After this lean state, runt the Mixture Screw counterclockwise until things smooth out and runs at maximum RPMs.  Now repeat with cylinder 4, 2 and 1.


If things are still rough, you may need to tweak things.  Popping in the carb or exhaust usually means it is too lean, while a slow unresponsiveness or black smoke suggests a rich state.  If you are maxing out your setting, you may need to rejet your carbs.


Now set you idle speed back down to 750 to 850 RPMs.


If everything up to this point is fine, it's time to check air flow at each barrel.  If they are all equal - you are done.  If your air measurements vary, they you and adjust the Air By-Pass Screws until they are all the same.  Air flow is increased by opening the Air By-Pass Screws and conversely, air flow is decreased by closing the Air By-Pass Screws.  The Air By-Pass Screws should be opened up no more than 1.5 turns from it bottomed out or you will get a too lean condition.


Install your air filters (with oil). Check that everything is in order and go for a ride.


Harvey's Carburetor Clinic

Redline IDF Carburetors Low Speed Circuit Tuning

KYMCO Webber IDF Adjustment



Weber IDF Parts Breakdown


Item # Quant Desc Part #   Item # Quant Desc Part #
1 1 Air Horn 52848.003   32 1 Pump Cover 32486.085
2 1 Pump Control Rod 61285.042   33 1 Pump Diaphragm 47407.207
3 1 Carburetor Top Cover 93.0078.05   34 1 Fixing Pin 58445.001
4 2 Stud 64955.108   35 1 Pump Diaphragm Spring 47600.250
5 1 Pump Rod Spring 47600.252   36 2 Vacuum Tube-Off Cover 61015.005
6 1 Carburetor Main Gasket 41705.085   37 2 Air By-Pass Screw 64750.029
7 1 Fuel Filter 37022.002   38 2 Air By-Pass Screw Nut 34705.001
8 1 Fuel Filter Gasket 41530.024   39 2 Throttle Plate 64005.126
9 1 Fuel Filter Cover 61002.010   40 4 Throttle Plate Fixing Screw 64520.027
10 2 Pump Demand Valve 64290.016   41 1 Air Horn Gasket 41655.020
11 4 Pump Jet Gasket 41530.012   42 1 Throttle Return Spring 47610.035
12 2 Pump Jet 76210.050   43 1 Throttle Lever 45034.109
13 1 Pump Spill 79701.055   44 2 Choke Tube Fixing Screw 64830.002
14 2 Auxiliary Venturi 69002.450   45 2 Choke Tube Fixing Screw Nut  34715.010
15 2 Venturi (Choke Tube) 71506.280   46 2 Fixing Screw 64700.013
16 2 Stud 64955.114   47 2 Main Jet 73401.115
17 1 Throttle Lever 45034.110   48 2 Emulsion Tube 61450.031
18 2 Throttle Spindle Nut 34710.003   49 2 Air Corrector Jet 77401.200
19 2 Lock Washer 55520.004   50 2 Emulsion Tube Holder 52580.006
20 2 Spring Ring 55530.005   51 1 Float 41030.008
21 2 Race Bearing 32650.003   52 1 Float Pin 52000.001
22 2 Idle Jet 74405.050   53 1 Needle Valve 79511.175
23 4 Idle Jet 'O' Ring 41565.002   54 1 Needle Valve Gasket 83102.100
24 2 Idle Jet Holder 52570.006   55 5 Top Cover Fixing Screw 64700.005
25 1 Throttle Stop Screw Spring 47600.007   56 1 Fuel Inlet Pipe 10525.023
26 1 Throttle Stop Screw 64625.015   57 1 Pump Adjustment Rod 12750.126
27 1 Pump Rod Spring 47600.251   58 1 Spring Clip 32610.003
28 2 Mixture Screw 'O' Ring Cap 58000.006   59 1 Pump Rod Nut 34725.008
29 2 Mixture Screw Spring 47600.062   60 2 Fuel Pipe Gasket 41535.003
30 2 Mixture Screw 64750.003   61 1 Threaded Cap 61002.022
31 4 Pump Cover Screw 64700.004   62 1 Throttle Shaft 10005.243


Original Specs 40 IDF 70
Main Jets 115   Emulsion Tubes F11
Air Corrector  Jets 200   Venturis 28mm
Idle Jets 050     Aux Venturis 4.50mm
Pump Jet 050   Needle Valve 1.75mm
Pump Exhaust Jet 055      


Weber IDF Dual Linkage


CB Performance - Weber Carbs - Dual IDF Kits

CB Performance - Upgrading Dual IDF Carburetor Linkage

Triadwest - 914 Carburetor Linkage - Weltmeister design

Gene Berg



Weber IDF Jetting Chart

This Jetting Chart provides a base line starting point provided by CB Performance. Every engine responds differently, and final jetting changes are most often determined by the engine builder or tuner. Engine size, cam, cylinder heads, ignition system, compression ratio, exhaust system, type of fuel, the vehicle and type of driving are all key elements in final calibration. The selection of main gas and air correction jets is determined by venturi size. The venturi sizes listed below are the sizes supplied by Weber in new carburetors. The use of larger venturi will increase airflow, and larger main gas jets than noted below will be required.


WEBER 40 IDF Factory
AIR CORRECTION 2.00 1.60 2.00



MAIN JET 1.15 1.45 1.30
PUMP JET .50 .80 .50
IDLE JET .50 .65 .55



NOTE: Drill 2mm Hole in each Throttle Valve of Single Carb.
WEBER 44 IDF Factory
AIR CORRECTION 1.75 1.65 2.00



MAIN JET 1.35 1.60 1.55
PUMP JET .50 .80 .50
IDLE JET .50 .65 .60



NOTE: Drill 2mm Hole in each Throttle Valve of Single Carb.
WEBER 48 IDF Factory
AIR CORRECTION 1.80 1.80 2.00



MAIN JET 1.50 1.70 1.75
PUMP JET .50 .80 .50
IDLE JET .55 .65 .60



NOTE: Drill 2mm Hole in each Throttle Valve of Single Carb.


CB Performance - Weber Carburetor Parts




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