Volkswagen Weber Progressive Carburetor

 

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Volkswagen Weber Progressive Carburetor

 

 


The Weber Progressive carbs can work great for a VW or be an utter nightmare, depending on how it is set up.  And unlike other double barreled carburetors, this one isn't designed with two synchronous barrels meant to feed separate halves of a V8 engine.  This double barrel system instead has a primary barrel used solely at low to half throttle operation and a second barrel that opens up when you increase your throttle allowing for increased air and fuel delivery at wide open throttle.  This allows of better low throttle economy with the option for increase performance on demand.  It can also make tuning more of a challenge than with single barrel and regular double barrel carburetors.

 

On VWs, these are generally used as center mount systems but there were kits sold in the past that allowed you to mount duals.

 

 

Manifold Heat - Stop VW Carb Icing

For fuel to be delivered to the combustion chambers ready to burn the fuel must be vaporized.  If your air fuel mixture isn't warm enough, you will need to run a much richer mixture to compensate for the fuel that condenses on its journey through the intake manifolds.  The pooling of this condensed fuel in the manifolds not only makes it challenging to tune your idle, but will sucked into the combustion chambers all at once when you open up the throttle creating a too rich burn condition.

 

In dual carburetor setups, the metered fuel only need to travel a very short distance straight down into the combustion chamber.  There isn't much time to cool down and the short length of the intake manifolds also don't take long to heat up from direct contact with the heads.  But dual Progressive setups are rare these days and kits are not longer made.

 

On the other hand, in a center mount progressive carburetor system, your metered air/fuel mixture must travel downwards a good distance and then make a 90 degree turn, travel some more and them make another 90 degree turn into the combustion chamber.  Only the very ends are in direct contact with the heated heads and the rest of the manifold can easily cool down due to all of its surface area exposed to air.  This setup makes it all too easy for fuel to condense on its way to the heads and a center mount progressive system must be heated for it to properly function.  Because of this, they won't work in a Type 4 VW.

 

The best working systems use heat from the exhaust.  The stock VW exhaust for Type 1 has one exhaust port that connects to the header's base where it connects to the #2 cylinder side of the right head (mirror image in Mexi Beetles) and one exhaust port that snakes its way into the muffler.  This allows a high pressure side and a low pressure side which in turn pushes hot exhaust gasses through the heat riser tubes into the manifold and out into the muffler.  Unfortunately, many aftermarket headers just have exhaust ports at the base of the #2 and #4 cylinders.  This gives a nice symmetrical look but basically only allows gasses to pulse back forth through the two sides of the heat riser tubes.  This pulsing doesn't allow for an efficient transfer of heat and can lead to premature carbon build up in the tubing and manifold.  

 

If you are using an aftermarket or custom exhaust, you will want to have one exhaust port at the base of one of your exhaust pipes and another exhaust tube that joins at the collector.  This will allow heat to travel from the base of one pipe, through one heat riser, into the intake manifold, out the other heat riser and into the collector.

 

High pressure exhaust port at base of #2 cylinder Low pressure exhaust port adjacent to #4 cylinder and into collector

 

Another heat option is to run warm engine oil through the manifold and back to the engine.  You will need to have a quality and cleaned out manifold and not one that is porous. 

 

 

Heated Manifolds

There are several options for heated manifold and quality and functionality varies greatly!  Ideally, you will want a manifold that runs heat through the bottom of the manifold, up to the base of where the carb sits and back down through the bottom so that the entire manifold is heated.  Red Line has a nice system that also has the proper linkage to allow for full open throttle on a VW without any accelerator modifications.

 

Most other heated manifolds just run heat through the bottom of the manifold itself.  These are generally not sufficient for reliable lower temperature (below 40 deg F) use.

 

Ref:

Cleaning a Carbon Clogged Heat Riser Tube

Why do I need to heat a center 2 bbl carb setup?

Tom's Bug Heat Riser

Not another Class 11 (style)...  Pictures of exhaust setup

 

 

Heated Air

Routing heated air to your carburetor helps.  You can simply use rain gutter downspouts to redirect heated air from under your heads to the air intake or get fancy with a heat collector around your exhaust.

 

Ref:

The Long Awaited Progressive Carb Warm Air Induction Post

 

 

Linkage

If your kit didn't come with special VW specific linkage, than you won't be able to use the progressive circuit unless you get this linkage, drill out a hole higher on your accelerator for the throttle cable, or get creative.

 

 

Carburetor Choices

Weber has a FDEV and a FDAV.  The FDEV has an electric choke and the FDAV has a water choke.  The FDEV is preferred for an air cooled VW since there isn't heated water to operate the FDAV.

 

There are also EMPI progressive knock offs.  The quality of EMPI carbs can be quite poor and these should be avoided.

 

 

Fuel Pressure

Weber carbs need 3-3.5 PSI of fuel pressure and properly set floats.

 

 

Jetting

Jetting can be problematic as different shops and drivers run a wide gamut of configurations.  For a progressive carburetor, only one barrel is open during the normal operating range.  When the second barrel opens up, the available amount of air running through each barrel drops, causing an overall decrease in carb vacuum.  To compensate for the decrease in air flow and vacuum through each barrel, the secondary jets need to be larger than the primary to compensate and prevent a lean state when the the progressive circuit opens.  And if you don't do this, John Connolly from aircooled.net will slap you upside your head.  Here are his recommendations:

 

Aircooled.net Jetting Recommendations

Elevation Pri Idle Sec Idle Pri Main Sec Main Pri Air Sec Air
Sea Level 45 60 125 190 160 180
4,000 Ft 45 55 120 180 175 190
8,000 Ft 40 55 115 175 190 205

 

If you aren't running a quality heated manifold, then you will need to compensate with a richer mixture and adjust your jets appropriately.

 

 

Carburetor Breakdown

 

32/36 DFEV PART NO. 22680.070

No Qty Description Part Number   No Qty Description Part Number
1 1 Carburetor Cover Assy Not Serviced   51 1 Screw Plug 61015.003
2 4 Stud Bolt 64955.002   52 1 Screw Securing Auto Choke Body 64700.015
3 5 Top Cover Fixing Screw 64700.005   53 1 Gasket For Auto Choke Body 41640.005
4 1 Top Cover Gasket 41705.034   54 1 Auto Choke Thermostat Assy 57804.076
5 1 Primary Air Corrector Jet 77201.*   54a 1 Electric Choke Thermostat 57804.332
5a 1 Secondary Ari Corrector Jet 77201.*   55 3 Thermostat Assy Locking Ring 52135.006
6 1 Pump Delivery Valve Assy 64290.024   56 1 Water Chamber Seal Gasket 41555.001
7 1 Primary Emulsion Tube 61440.*   57 1 Water Cover Fixing Screw 64615.001
7a 1 Secondary Emulsion Tube 61440.*   58 1 Gasket For Screw 41530.002
8 2 Pump Jet Gasket 41540.014   59 1 Auto Choke Water Chamber 32444.010
9 1 Accelerator Pump Jet 76211.*   60 1 Choke Shaft & Lever Assy 10085.031
10 1 Power Valve Assy 57804.025   61 3 Screw Securing Auto Choke Cover 64700.007
11 1 Needle & Seat 79519.*   62 1 Spring Retaining Cover 58000.018
12 1 Float Fixing Pin 52000.015   63 1 Spring Washer Not Serviced
13 1 Plastic Float 41030.022   64 1 Fixing Nut Not Serviced
14 1 Primary Idle Jet 74403.*   65 2 Screw Securing Auto Choke Body 64700.023
14a 1 Secondary Idle Jet 74403.*   66 1 Plate For Choke Shaft 52130.012
15 2 Idle Jet Holder 52570.005   67 1 Washer For Shaft 55555.029
16 1 Carb Body Not Available   68 1 Idle Adjusting Screw 64750.001
17 1 Secondary Throttle Control Lever 45032.013   69 1 Spring For Idle Adjusting Screw 47600.007
18 1 Flat Washer 55510.046   70 1 Gasket For Auto Choke Body 41565.008
19 1 Spring Washer 55525.001   71 1 Accelerator Pump Cover Assy 32486.034
20 1 Fixing Nut 34705.001   72 4 Pump Cover Fixing Screw 64700.004
21 1 Spring For Loose Lever 47605.010   73 1 Accelerator Pump Diaphragm Assy 47407.261
22 1 Primary Loose Lever Assy 45069.006   74 1 Pump Loading Spring 47600.107
23 1 Flat Washer 55510.061   75 4 Throttle Valve Fixing Screw 64520.023
24 1 Throttle Control Lever Not Serviced   76 1 Primary Throttle Valve 64005.090
25 1 Lock Washer 55520.002   77 1 Primary Main Shaft Assy Not Serviced
26 1 Fixing Nut 34715.014   77a 1 Primary Main Shaft Assy Oversize 10016.475
27 1 Bushing For Loose Lever 12765.002   78 1 Secondary Main Shaft Assy 10015.413
28 1 Lever For Throttle Adjusting Screw

Including:

Not Serviced   79 1 Secondary Throttle Valve 64005.034
29 1   -Lever 45039.022   80 1 Primary Main Jet 73801.*
30 1   -Spring 47600.073   80a 1 Secondary Main Jet 73801.*
31 1   -Screw 64625.006   81 1 Power Valve Gasket 41530.013
32 1 Secondary Throttle Adjusting Screw 64595.005   82 1 Full Power Need Valve 64235.016
33 1 Primary Shaft Return Spring 47610.012   83 1 Gasket For Needle Valve 83102.070
34 1 Washer 55555.016   84 3 Power Valve Fixing Screw 64700.007
35 1 Fast Idling Loose Lever

Including:

Not Serviced   85 1 Strainer Inspection Plug 61002.018
36 1   -Screw 64590.004   86 1 Locking Ring 10140.501
37 1   -Spring 47600.007   88 1 Choke Shaft & Lever Assy 10020.214
38 1   -Lever Not Serviced   89 4 Choke Plates Fixing Screw 64525.003
39 1 Screw Securing Fast Idle Loose Lever 64700.014   90 1 Dust Seal Plug 61070.002
40 1 Bushing For Fast Idle Loose Lever 12765.042   91 1 Dust Seal Plate 52135.018
41 1 Washer 55530.005   92 1 Strainer Assy 37022.010
42 1 Fast Idling Control Rod 61280.042   93 2 Choke Throttle Valve 64010.006
43 1 Flat Washer 55510.003   94 3 Screw For Thermostat Plate 64615.005
44 1 Choke Shaft Control Lever Not Serviced   95 1 Pump Discharge Blanking Needle 64900.001
45 1 Spring For Fast Idle Cam 47610.083   96 3 Flat Washer 55510.038
46 3 Auto Choke Body Assy 57804.072   97 2 Auxiliary Venturi 71110.*
47 1 Choke Diaphragm Assy 47407.080   98 1 Choke Device 35-52; 61-67 57804.119
48 1 Spring For Diaphragm 47600.141       *Calibrated Parts Require 3 Digits To  
49 1 Cover For Choke Diaphragm 32384.022       Complete Part Number  
50 1 Diaphragm Adjusting Screw 64595.005       See Calibrated Parts Section For Sizes.  

 

 


 

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