48IDF carburetor

Specifications

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  Pre-tuning

  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.

   

   

  Install

  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.

   

   

  Synchronization

  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.

   

   

  Tuning

  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

   

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  CB Performance - Weber Carbs - Dual IDF Kits

  CB Performance - Upgrading Dual IDF Carburetor Linkage

  Triadwest - 914 Carburetor Linkage - Weltmeister design

  Gene Berg

   

   

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  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 Sizes	Single Carb	Dual Carbs
  AIR CORRECTION	2.00	1.60	2.00
  EMULSION TUBE	F-11
  MAIN JET	1.15	1.45	1.30
  PUMP JET	.50	.80	.50
  IDLE JET	.50	.65	.55
  VENTURI	28mm
  NOTE: Drill 2mm Hole in each Throttle Valve of Single Carb.
  WEBER 44 IDF	Factory Sizes	Single Carb	Dual Carbs
  AIR CORRECTION	1.75	1.65	2.00
  EMULSION TUBE	F-11
  MAIN JET	1.35	1.60	1.55
  PUMP JET	.50	.80	.50
  IDLE JET	.50	.65	.60
  VENTURI	36mm
  NOTE: Drill 2mm Hole in each Throttle Valve of Single Carb.
  WEBER 48 IDF	Factory Sizes	Single Carb	Dual Carbs
  AIR CORRECTION	1.80	1.80	2.00
  EMULSION TUBE	F-2
  MAIN JET	1.50	1.70	1.75
  PUMP JET	.50	.80	.50
  IDLE JET	.55	.65	.60
  VENTURI	40mm
  NOTE: Drill 2mm Hole in each Throttle Valve of Single Carb.