By the time Volkswagens were “in the womb”, carburetion was not a new thing. But the German Engineers tasked with creating a viable engine system for Ferdinand Porsche had to create a system that would work with the air-cooled engines which were being demanded. Bit by bit, the VW carburetors were evolving into what would become a virtually fool-proof unit.
With the advent of the 12 Volt Electrical System, Volkswagen was coming of age. Carburetion would be just one of the areas which would benefit—with better starting possibilities. Let’s look at the Choke Mechanism on the VW 105-1 30 Pict-1 Carburetor.
While there are several parts to the Choke Mechanism, it is relatively simple.
But first—what is meant by “choking the engine”? “Choking” might better be termed “restricting”—because that’s what’s happening. When the Engine is dead cold, the Fuel Mixture must be more “rich” in gasoline with less air. The Engine is “hungry”. So, by restricting (or choking) the in-coming air, this need can be met.
Eventually, in a matter of minutes, the Engine will be running well and will need more air in the Fuel Mixture as it begins to reach operational temperature. It will be “starving” for air. Now the restriction on air can be relaxed—the “choke-hold” can be relaxed and the Carburetor can seek its own Fuel Mixture levels as needed.
We will be examining only the Upper Half of a Carburetor during this discussion of the “processes” or elements which comprise the Choking Mechanism.
First, let’s examine the Choke Element: The Choke Element is a simplified heating element consisting of a tiny wire Coil much like the larger coils in a toaster or an electric space heater—but it is tiny. This Coil is housed inside a round metal and ceramic disc which has an Electrical Connector. Onto this Connector is connected a wire which comes from the Positive Pole (#15) Terminal of the Engine Coil. This is the power source for the Choke Element.
The Choke Element is grounded on the Carburetor, which is grounded to the Engine, which is grounded to the Chassis and so forth—completing the necessary electrical circuit.
Inside the Choke Element, is a Bi-metal Flat Spring with a hook on its loose end. Once the Key is turned to the On Position at the Ignition Switch, power flows to the Choke Element’s tiny wire Coil, causing it to glow. The glowing Element slowly heats the Bi-metal Spring, causing it to “relax” its hold on the Choke Plate Shaft Upper Arm—which allows the Choke Plate to open.
Sound complicated? It’s really not. It’s simply one thing causing another to react, doing the intended job. In the earlier years of carburetion, there had been a cable from a carburetor to the dash knob of a vehicle—any vehicle. The driver would pull the knob, activating the manual choke—restricting air flow into the carburetor. As the engine warmed, the driver (when he remembered) would push the knob in, allowing more air to enter the carburetor. At age 14, this was how I did it on the family 1949 Ford V-8. I distinctly recall doing that operation, especially in cold weather.
Auto makers wanted to by-pass human thought in order to have the engine to automatically choke the carburetor. Thus, eventually, had been born the “Automatic Choke”.
That is the principle and that is the chief activation mechanism for the 30 Pict-1 Carburetor Choke.
Let’s look at the parts associated with the over-all Mechanism. I removed a Choke Plate and Shaft from a Carburetor for comparative purposes. In the photo below we can see the bare Shaft and Choke Plate.
Starting inside the Carburetor Choke Mechanism Recess on the Carburetor Housing, we find the end of the Choke Plate Shaft with the Upper Arm which the Bi-metal Spring activates during the heating process.
Working outward, we next see the Bakelite (plastic) Insulating Cup. The Cup has a tab which fits a groove inside the Housing to keep it in place. A slot allows the Choke Plate Shaft Upper Arm to protrude. The Bakelite Cup keeps heat from dissipating from the Heating Coil. Otherwise, heat loss would thwart the Heating Coil’s efforts upon the Choke Plate.
Next comes the Heating Element itself which is inserted into the Carburetor Housing. The Heating Element must be rotated so that the Bi-metal Spring Hook catches on the Choke Plate Shaft Upper Arm.
To secure the Heating Element to the Carburetor a metal Retaining Ring (or Bezel) with 3 holes fits over the Heating Element. Three Screws with 3 Plastic Cylindrical Spacers are used to secure the Bezel to the Carburetor Housing. Thus, the Heating Element can be rotated clockwise or counter-clockwise, as necessary, when adjusting it. Loosen the 3 Screws and the Heating Element can be rotated to the proper position. Then, the 3 Screws are tightened to fix the position of the Heating Element.
While this Process is activated……there is a Second Process at work. It is called the “Choke Pull-off Diaphragm” or the Vacuum Diaphragm. The purpose of this part is to “moderate” the action of the Choke Heating Element.
While the Choke Plate is Closed and the Fuel Mixture is “rich” in gasoline and “poor” in air, the Choke Heating Element is slowly relaxing its hold on the Closed Choke Plate.
During this slow heating-and-relaxing process, the Vacuum Diaphragm comes into play.
As the Accelerator Pedal is activated by the driver of the car, vacuum is achieved as air rushes through the Carburetor. Part of this vacuum “sucks” through various drillings (or passages) in the Body of the Carburetor. One of these drillings connects to the Vacuum Diaphragm. Vacuum “sucks” the Vacuum Diaphragm, pulling its Shaft.
As the Vacuum Diaphragm Shaft pulls, it catches the end of the Choke Plate Shaft Lower Arm so that the Choke Plate is pulled slightly open. Thus a bit more air can be sucked into the Carburetor as the car begins to drive and the Engine needs more air with the Fuel Mixture.
The operation of the Vacuum Diaphragm may seem to be insignificant. However, especially at start-up, it is needed to moderate the choking action exerted upon the Carburetor by the Heating Element.
There was no such apparatus on that afore-mentioned ’49 Ford. You pulled the choke knob and restricted the air to the fuel mixture more or less—as YOU thought necessary. There was no automatic “moderating” counter-force available.
Part II is coming. Part II will examine the Automatic Choke Adjustment Process.
My thanks to David Brown who graciously discussed Carburetor parts and, especially, the Vacuum Diaphragm and its necessary function.
Neva and I worked to get some photos to illustrate how everything goes together. There’s no better way to understanding something than to reduce it to its fundamental parts. Neva listened patiently as I used her as a captive audience while I explained parts and functions. Now—that’s a dedicated wife and VW enthusiast!
Comments are closed.
Hi Jay, thanks for the great post. I’ve noticed when I start my car and let it run for a bit in the driveway it seems to rev pretty high until I tap the gas pedal. The engine then slows down to a normal idle. Is this normal? Seems like I shouldn’t have to tap the gas pedal. Is my choke operating correctly? Thanks again!
Hello, Daniel. Thank you for posting here. It is not unusual for the idle cam to be hesitant about clicking to the next stop. There could be a “couple” of things at work there. In my Part II, I will address issues regarding start-up and the carburetor idle adjustment. I see that I need to get cracking to complete this study. Stay tuned! jay
You have to hit the gas pedal to get the idle down. When you step on the gas once in the morning the carb gets set on high idle cam. The car runs in a rich state because of the choke. When the idle starts getting high tap the gas pedal and the idle will drop and the cam will be engaged to lower and lower positions until its warmed up.
Hello, Frank…It is so good to hear from you! You hit the nail right on the head. As the car is driven down the road, the action at the accelerator pedal keeps allowing the idle cam to kick to the next step down. I have in mind to continue this conversation in my next Part. I hope that all is well with you and the Family! Stay warm up there in snow-country! jay
Hi Jay! Hope all is well. My bug is hibernating. There is salt all over the roads for the past several months!
Frank…I hear you! I regularly communicate with several VW Owners who have put their cars away for the duration. One lone die-hard who will drive his ’67 Bug but he’s always washing it to remove any residue. I think that you folks there just got a fresh snow-fall. Wild Winter, it is, Frank! jay
Thanks Francis, that’s what I figured but I wasn’t sure if it was supposed to be automatic and related to the choke. Glad I asked. Thanks again for the great post Jay. Looking forward to part 2!
Its a mechanical linkage. Auto nothing really. The can and linkage needs input from the gas pedal/throttle cable to pull the idle down. Perfectly normal.
Thanks Jay for a great informative article. Kind of wish I had it when I was muddling through the rebuild on my 30 Pict-2
Hi, David…I always learn lots from studying a particular subject or part. I wish that I had put more thought into studying VWs when I was younger–but, then–I was working and had little time for digesting more than just maintenance. Not only so, but it was not possible where I live to have such a huge association of VW people as it is today with the InterNet. Isn’t it great! jay
You are too generous, Amanda! Maybe someone will get the same joy from knowing about these parts that I did, learning more about them. jay
Hello from Germany.
I’ve been reading Jay’s articles for the last 4 years at this 1967 VW site. Yourself and Mr Shoemaker are the modern day VW encyclopedia for us folks that need to keep our cars on the road.
Hello, Adalbert…thank you for your most gracious comments! It is so wonderful of Eric and Amanda to maintain this Site for us in the 1967 Beetle Community! There are so many ’67 Beetle Owners who have so much wisdom to impart. When someone asks me a question about a ’67 (and for some of the other years as well), I can refer them to an appropriate Link. It’s a great feeling to be in the company of so many talented VW Owners! Thanks for staying in touch. Let’s hear more from Germany! jay
Love this! I found a good 105-1 for my 1967. It’s the only non-original part on the car. I bought it from a one owner who pulled it behind their RV. The info about carbs I’ve seen on here is great! Much appreciation!
Wow, Jason. Isn’t it great to find another piece to the puzzle. The 105s have become a bit scarce. I know that Eric combs the InterNet constantly to locate more of them. I love these little carbs–they are so reliable and simple to manage. One of these days, you need to get Your Story to Eric for publication. Let the rest of the ’67 Community read Your Story! jay
The 67 German Solex 30-1 with the base flange number of 105-1 is in my opinion the best carb VW installed on any VW. In 1968, VW transitioned to the finicky Solex 30-2 carb with it’s none adjustable metering screw deep inside it. The 30-2 also was the first year to have the extra arm next to the throttle arm to hook up the throttle positioner which was VW’s first attempt at smog reduction. I have both these carbs on my bone stock VW’s. Both have had the throttle shaft bushings replaced and have been restored. By far, the 30-1 is much less finicky and is very low maintenance compared to the 30-2. I also run the notorious Solex 34-3 carb that in my opinion gets a bad rap. It’s a great carb as long as the throttle shaft bushings are not leaking vacuum and it’s matched to the correct distributor with the correct vacuum canister.
The good news is VW delivered over 900k 67 beatles world wide. Even though this 1967 only carb is heavily coveted, it’s really not that rare or hard to find. There’s still thousands of used ones out there waiting to be restored and put back in service. I still see them all the time at the larger VW swap meets.
Hello, Bill…I agree with you–the 105-1 is a great, reliable Carburetor! AND–I agree with you when you say that these Carbs should be matched to their designated Distributor. They have run for me trouble-free for hundreds of thousands of miles. Although there are a great many 30 Pict-1 Carbs out there, I rarely can find any of the VW 105-1s anywhere. I know that Eric has been scouring the Country for them with little success. Mostly, he finds the 30 Pict-1s for either the 6 volt series or for ’67 applications for Ghias or Buses. When you find a true 105-1, let Eric know. Keep singing the “song” for the 1967 Beetle, Bill! It’s a great “tune”! jay
Hello, it’s been 10 months, has any body followed up with Part Two – adjusting the choke? A search is not bringing it up. Thanks
Hello, Chris–you are a Loyal Reader! I have the script and the photos–only one part lacking and I will see if Eric will post Part II.
I apologize for the long delay! I try to use my illness as an excuse! But, it’s no use–I’ve just not done my part. Thank you for waiting, Chris! jay
Still waiting for part II. Any response, site moderator(s)? As Fall is now here Part II would be helpful. Thanks