With colder weather, especially, the Chokes on our 1967 Beetles with the 30 Pict-1 Carburetors play an even more important part in the starting of the car. We want the Choke Plate to be closed so that there will be a more rich fuel mixture to kick-start the Engine and get it to running temperature.
Given that the Electric Choke Element is in working condition—we want to get into our cars, press the Accelerator Pedal once and let up. This allows the Spring in the Electric Choke Element to snap the Choke Plate closed. Although we can’t see this happening while the Air Breather is on the Carburetor, we CAN see that this is happening by looking at the Idle Cam position.
When we step on the Accelerator Pedal, the Accelerator Lever is pulled back, allowing the Idle Cam to move freely. Now, the Idle Cam snaps to its highest position. The Accelerator Idle Screw is resting, now, on the highest Step on the Cam.
The Engine is racing. But, this is good! It is running at higher RPMs, sucking in that gasoline rich fuel mixture in order to bring the Engine to running temperature.
But, we don’t want this to continue on and on and on. As the Choke Heater Element becomes hotter, it begins to release tension on the Bi-metal Spring, allowing the Choke Plate to slowly open.
The vibration of the running engine, coupled with the foot action at the Accelerator Pedal, allows the Idle Cam to slip to a lower position. The Choke Plate opens more and more until it is pointing almost straight up, allowing more and more air to mix with the fuel.
This process continues until, eventually, the Idle Screw is resting on a low Cam Step and the Engine is idling at a lower speed. The Electric Choke has done its job well.
But what happens when the Engine continues to run and run and run at high speed and the Idle Cam doesn’t move. And—nothing that we do seems to help it to move—apart from manually moving it. Something is not right.
It is possible, also, that the Choke Plate Shaft can stick at Low Idle or anywhere along the Idle scale.
As our Engines operate, Fuel Residue builds on the Choke Plate Shaft. Eventually this gummy residue can cause the Shaft to stick. And, even though the Choke Spring has released tension on the Plate, the Plate cannot move to the open position.
One method which may help is to spray Carburetor Cleaner directly onto the Shaft behind the Idle Cam. Often this is sufficient to loosen and wash-away residue. Aerosol Carburetor Cleaner sprays can be obtained at any local parts store, with plenty of choices available.
Remove the Air Breather. Spray liberally every where the Choke Plate Shaft and the Carburetor Body intersect. Move the Idle Cam as you spray to see if the spray is being effective.
This may not be sufficient to completely remove residue and allow free movement to the Choke Plate Shaft.
Note: Restriction of the Idle Cam also may be caused when the Limiter Pin becomes jammed in the curved slot of the Idle Cam. It is possible that the Pin may have become bent, perhaps just from years of use. The original Pins were brass. The Pin can be straightened or a substitute steel roll pin can be installed. This may involve drilling to enlarge the Pin’s anchoring hole. A new Pin should be sized carefully so that it will fit the slot as the Idle Cam pivots and not cause binding because it is too large in diameter. I used to make my own brass Pins when one would be lost or bent or broken.
Other causes of binding of the Idle Cam can include corrosion or dirt in the Choke Plate Shaft’s Bore.
If all efforts of spraying a solvent at the Choke Plate Shaft fail to loosen the Shaft and allow it to rotate freely, a thorough cleaning is warranted. This requires removal of the top of the Carburetor.
You don’t have to remove the Carburetor from the engine, but it makes the work easier, in my opinion. Once the Fuel Hose has been removed, and the Accelerator Cable, the Accelerator Lever Return Spring and the electric wire to the Choke Heater have been removed, use a 13mm end wrench to loosen and remove the two securing nuts at the Manifold.
With the Carburetor in hand……..
Remove the Electric Choke Heater parts.
Remove the Choke Vacuum parts.
Using a 10mm closed end wrench, remove the nut securing the Choke Plate Lever and the Idle Cam to the Choke Plate Shaft. See the photo below which reveals the parts in their order of removal/installation.
Review the Brass Bushing. If it appears to be less than smooth where the Idle Cam fits over it, use some very fine wet-dry abrasive paper to polish it. I use 1000 grit, or finer, commonly. Use the same polishing technique on the end of the Choke Plate Shaft where the Bushing fits.
Remove the 5 retaining screws which secure the top of the Carburetor to the bottom half (Throttle Body). Carefully lift the top, taking care not to damage the gasket between the top and bottom halves. It can be reused if it is undamaged in this process.
Remove the Float Valve—14mm end wrench.
Note: Do NOT attempt to remove the two Retaining Screws which hold the Choke Plate to the Shaft. These Screws have been installed at the factory so that they will not loosen and be sucked into the combustion chambers where they can cause major damage.
Photograph #64 shows a Choke Plate and Shaft (for comparison) removed from an identical Carburetor.
Cleaning can be accomplished by putting the Carburetor top into a can of Carburetor Cleaning Solution. A half day usually is enough time for the cleaning to take place.
*All cleaners should be used outdoors where there is plenty of ventilation. Use protective gloves.
After using a Carburetor Soaking Solution, follow the directions on the container for removing residual Cleaning Solution.
If you use an aerosol spray, spray the Choke Shaft liberally, working the Shaft as you spray.
Once cleaned, the Shaft should turn freely—with NO resistance.
The Shaft and its Bore can be lubricated with a few drops of anti-corrosion oil. Work the Shaft several times to ensure proper dispersal of the lubricant.
While you have the top half of the Carburetor removed, clean all outer surfaces well.
Reassemble in reverse order.
Start with the Choke Plate Shaft fittings at the Idle Cam Side. Be sure that the Nylon Washer on the Choke Plate Shaft is fitted over the Brass Bushing and not pinched between it and the body of the Carburetor Top.
Once these parts have been reassembled, check movement. Is the Choke Shaft turning freely? Is the Idle Cam moving freely? If not, determine why not before continuing reassembly. This is the condition which we wanted to remedy when we began this exercise.
When you are satisfied with your cleaning efforts, reassemble the rest of the Top’s parts.
Then reattach the Top to the Throttle Body (bottom half of the Carburetor). Do not over-tighten the screws!
Bolt the Carburetor onto the manifold and reinstall the Accelerator Cable. Properly adjust the Choke Heater Setting, and reinstall the Electric Wire to the Choke Heater.
If the work has been done properly and there is no physical reason for the Choke Plate not to function properly, you should have plenty of trouble free driving for many months or years to come.