I would like to thank Jim Thompson of AirHead Parts and Bob Ellis for letting us use this info on Shoptalkforums.
Jim& Bob wrote:
Type-1 Carburetors thru the years and how to rebuild and troubleshoot them.
Nine different carburetors were used during the post war period of beetle production.
The first three were the 26VFI, 26VFIS and the 28PCI. These antiques are becoming rare and are seldom used or seen any more. The procedures and repair described below apply to these also, but instead, have a mechanical choke, and the VFI and VFIS are not equipped with an accelerator pump. Additionally, the venturi was removable to allow it to be changed to different sizes depending on the model used on.
28 PICT (1961-1963)
This was the first Volkswagen that featured a ceramic electric choke. It features a piston that opens the choke butterfly slightly when the engine is started. Beginning with the PICT models, the venture was not removable.
28 PICT-1 (1964 -1965)
This model is the same as the previous except the piston was replaced with a vacuum diaphragm. The electric choke element was slightly enlarged and was encased in metal instead of ceramic. There is also no power circuit.
30 PICT-1 (1966-1967)
Same as above but with a slightly larger venturi and throttle bore. This was the last carburetor of the “Round Float Bowl” configuration.
30PICT-2 (1968-1969)
The first of the “Square Float Bowl” carburetors, designed for US Emission Controls (M Code M157). Internally, this model is similar to the previous but has a power circuit that draws fuel directly from the float bowl under full load conditions. It also featured an idle cut-off pilot jet valve.
30 PICT-3 (1970)
This model is also similar to the previous, but this one has an air bypass system that allows the throttle to close completely at idle and supplies idle air, provided by the bypass. The idle cut-off pilot jet valve was unique to this carburetor and not interchangeable with previous or subsequent models.
34 PICT-3 and 4 (1971-1974)
These two carburetors are similar to the previous, except they feature a bypass mixture cutoff valve instead of an idle cut-off pilot jet valve. The venturi was also increased for the dual port engine. Choke parts are not interchangeable (except for the bi-metal element). The Accelerator Pump is larger on the 34PICT-4. The 34PICT-4 was only installed on 1974 California Beetles & Super Beetles.
I have a few words of advice before you tear into your carburetor though, as most running problems can be traced to ignition issues. Make sure that your ignition is in good working order before you start blaming the carburetor. After removing the carburetor, check for throttle shaft play. If yours has play, it is most times better to buy a new one or find another carburetor to rebuild. The shaft has no bushings and tends to wear out over many years of use. They can be re-bushed by companies like Rimco, but I would only do that to an antique carb.
DISASSEMBLY
Clean off the work area that you plan on using. A sterile work environment is the key to a quality job.
Lay a towel or any CLEAN cloth over your work area to keep small, dropped parts from bouncing away on you. I have been known to rebuild carbs on the kitchen table, but this is not advisable unless you are or want to be a bachelor.
Some more tips:
Note the location of jets and small parts.
Make sure wrenches and screwdrivers fit exactly. Rounded bolt heads and screwed up screwdriver slots do not win show points.
Lay out all parts out in order to ease in reassembly.
There is no need to remove linkage and choke shafts unless they are damaged. Replacement parts are unavailable.
Do not use wire or drill bits to clean orifices.
INSPECTION
After disassembly clean all parts in solvent or better yet in a bucket of dip-in carb cleaner. This is your best bet, if you want your carb as clean as possible. Available at most full service auto parts stores.
Do not put anything except metal parts in the dip solution; it will melt gaskets and rubber o-rings
Wear rubber (not latex) gloves and protective clothing.
Check the float bowl needle and seat for wear. The needle valve is included in most rebuild kits. Replace it.
Immerse the float in hot water. If the float is leaking, bubbles will appear. Do not try to repair leaks in the float though. Soldering will add to the weight of the float, and the later plastic ones are totally un-repairable.
Check the idle mixture screw for wear at the tip. Replace if needed.
Blow out all jets and passages with compressed air. You can buy compressed air in a spray can at most shops that sell electronics.
Check the tapered portion of the air bypass screw if your carburetor is so equipped. Replace if needed.
Be sure to carefully replace the O-Rings on the Air Bypass and Volume Control (Mixture) Screws if your carburetor is so equipped.
These seldom wear but it can happen if they are torqued in too hard.
Replace all diaphragms.
Remember, BE CLEAN!!!!!!!
ASSEMBLY
Assembly is the reverse of disassembly but observe the following.
Align the mark on the choke body with the center mark on the choke housing, and be sure that the choke engages the lever.
On carburetors except for those listed below, install the Volume Control Screw (Mixture) and turn it in clockwise until it comes to a stop, then turn it counter-clockwise 3 turns.
On 30PICT-3, 34PICT-3 and 34PICT-4 carburetors, install the Volume Control Screw (Mixture) and turn it clockwise until it comes to a stop, then turn it counter-clockwise 2½ to 3 turns.
On 30PICT-3, 34PICT-3 and 34PICT-4 carburetors, install the larger Air Bypass Screw (Idle Adjustment) and turn it clockwise until it comes to a stop, then turn it counter-clockwise about 4 turns.
Do not over tighten the air cleaner strap, as this could bind the choke from distortion of the air horn.
If your model is equipped with a fuel shutoff valve, check for straightness of the rod and operation of the solenoid by attaching the wire to it and listening for a click when power is turned on. Airhead Parts have these in stock.
Use a new Manifold to Carburetor Gasket.
Lube all linkages with light grade oil.
ADJUSTMENT
Note: Adjustments are to be made with the engine fully warmed up. VW Factory Specification is for the Oil Temperature to be between 122 & 158 degrees.
On early carburetors (26VFI, 26VFIS, 28PCI), adjust the Idle Control Screw so that the engine runs at 550rpm. Gradually turn the Volume Control Screw (Idle Mixture) clockwise until the engine begins to slow down. From this position, turn the screw counter-clockwise until the engine reaches the fastest obtainable idle. If necessary, readjust the Idle Control Screw so that the engine returns to 550rpm.
On later carburetors (28PICT, 28PICT-1, 30PICT-1, 30PICT-2), the procedure is the same as above, except the idle speed is set at 850rpm (+ or – 50rpm)
On the later “Square Float Bowl” carburetors (30PICT-3, 34PICT-3, 34PICT-4), the procedure is substantially different. After warming up the engine, turn it off. Be sure the Automatic Choke is fully open. The screw on the end of the Throttle Arm is NOT an idle adjustment screw, but is adjusted to act as a Throttle Stop Screw against the Automatic Choke’s Fast Idle “stepped” Cam. Turn the Throttle Stop Screw counter-clockwise until there is clearance between the tip and the cam. Then turn the screw clockwise until it just touches the cam. From this position, turn the screw one-quarter turn clockwise. What this does is set the Throttle Butterfly to its proper clearance.
Restart the engine and after its re-warm-up, note the idle and if necessary, turn the large Air Bypass Screw to adjust to 850rpm. Turning the screw clockwise DECREASES the idle speed and counter-clockwise INCREASES the idle speed.
Now turn the smaller Volume Control Screw (Idle Mixture) counter-clockwise to the fastest obtainable idle (usually 2 to 3 turns, but sometimes there may be no change). Then turn this screw clockwise until the engine speed just slightly drops 20 to 30rpm. Readjust the Idle speed at the large Air Bypass Screw to 850rpm (+ or – 50rpm).
NOTE: This procedure is also the same with Brosol H30/31PICT carburetors.
HESITATION? – HELPFUL TIP
On 28PICT, 30PICT and 34PICT series carburetors, there is a small brass tube that’s located just below the Choke Butterfly Shaft called an “Injector Tube” (aka Fuel Dump Tube). Be sure the direction of the injected fuel spray is in the proper direction.
On 28PICT series, 30PICT-1 & 30PICT-2 carburetors, position the tube so that the injected fuel spray shoots straight down the throat.
On 30PICT-3 & 34PICT series carburetors, position the tube so that the injected fuel spray hits the fuel discharge tube, located further down the carb throat so that it “splatters”.
ENJOY YOUR WELL TUNED CAR!
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