A Volkswagen friend in England recently e-messaged me about a situation with his carburetor. His is a 28 Pict-1 but the situation is identical to that of the 30 Pict-1 carburetor.
The proposed problem deals with the Main Jet of the carburetor.
When my friend experienced some carb problems, he began to search the Internet for helps. He discovered a video and watched it and followed the instructions.
When the video came to the Main Jet installation, the mechanic pointedly explained that the hole in the Main Jet Carrier Bolt should align with the hole in the bowl of the carburetor.
My friend attempted to get the holes to align but was unable to do so. Now, he thought that he had a problem. He asked me if he should not tighten the Carrier Bolt, but leave it a little loose so that the holes would align.
By not tightening the Main Jet Carrier Bolt, gasoline will seep to the outside of the carburetor, resulting in the problem of raw gasoline in the engine compartment—a problem which none of us wants.
In the Carburetors mentioned above, the brass Main Jet Carrier Bolt also serves as the Plug for the bottom of the Carburetor Bowl. (Later carburetors have a simple steel or brass Bowl Plug. The Main Jet was separated from the Carrier Bolt and moved to a new location but has the same function).
With the Main Jet Carrier Bolt in hand, note that the area which has the holes is recessed—of a smaller diameter than the rest of the Bolt. There are three holes drilled on opposite sides of one another. This is so that gasoline can pass through the hole in the bottom of the Carburetor Bowl and enter the recessed area where the Main Jet Carrier Bolt resides. With the Main Jet Carrier Bolt installed, gasoline in the Bowl can freely circulate around the Carrier Bolt and enter the 3 drillings in order to pass to the Main Jet.
In the end of the Main Jet Carrier Bolt, is the Main Jet itself. It is screwed right into the Carrier Bolt. The gasoline which has passed from the Bowl into the Carrier Bolt now can be drawn through the Main Jet.
This gasoline continues its journey through a passage in the body of the carburetor into a chamber where it will be “emulsified”. The emulsification process mixes air and gasoline so that it can be more easily atomized through the Emulsifier Dispensing Tube
and sent down the throat of the carburetor.
The Emulsion Tube is a combination part consisting of the Tube Portion—which is the emulsifying agent and the Air Correction Jet.
The Tube portion has graduated holes which aid the emulsification process.
The Air Correction Jet—the portion which we see once the part has been screwed into its chamber—meters the air which is drawn through this Jet and into the emulsifying tube below it. This Jet has a stamping which indicates the size of the Jet’s orifice. Each Carburetor came from the factory with a particular size of Jet orifice. Usually this size will be fine, even if the Main Jet size is altered.
The emulsified gasoline-air now passes through the Dispensing Tube—which is part of the casting of the lower carburetor body. This tube is aimed downward so that the emulsified gas-air can pass directly past the Throttle Plate and into the manifold and onward to the Combustion Chambers.
How does this process work? By Vacuum!
Once the engine has started, there is a tremendous amount of vacuum generated. As the Pistons pump back and forth, they are pulling a vacuum through the manifold. This vacuum pulls air through the Air Correction Jet simultaneously creating a vacuum within the Emulsion Tube which in turn is pulling a vacuum through the Main Jet, through the Carrier Bolt Chamber and drawing gasoline from the Bowl into this System.
Once the Engine is running, the process is continuous, providing fuel to the Combustion Chambers for feeding the Combustion Process.
Early in the history of gasoline engines, the “carburetor” simply was an “atomizer”, working off the principle of a perfume spray bottle. Just as squeezing and releasing the bulb of a perfume bottle provides vacuum, pulling the perfume from the container and then expelling it, so it was with the early carburetors. With time and experience, modifications continued over the years to bring us the carburetor we use in our 1967 Beetles today. For anyone in need, Lane Russell has the correct 30 PICT 1 in stock.
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Another great article from Jay! Thank you for your contributions to the ’67 Beetle community.
Great article Jay!
Hi, Dick—thank you for the comment! I had fun with the article. What I learned, I thought might be of interest to others. Not everyone wants to know about the internals of a carburetor but the pictures are interesting! LOL Take care of your 3 Volkswagens! jay
Jay your article is “AAA” rated in my estimation as I learned a lot and look forward to applying your wisdom this winter as the Beetle is in storage. Moreover, I am amazed at the detail and clarity of the photos you used that compliment your narrative. Very useful for us weekend warriors!
Thank Neva for the photos, Gavin! Also, the local VW Guru, Barry Blythe, patiently listened as I explained to him how I thought the internals worked. He would correct me as necessary. Although the 30 Pict-1 is a “simple” carburetor, those Solex engineers were fixated with providing an excellent but inexpensive unit for our cars. We who still use them are using “ancient” technology coupled with 50 year-old units. I love these carbs! jay
It goes without saying Jay “behind every great man is a greater woman!”
Well done Neva, and thank you! Your skills here are much appreciated!
Best Volkswagen site on the web. Hello from Germany.
Hello, Anja. We are so happy to hear from you. We always are amazed at the far-reaching readership of 1967beetle.com Let us hear from you more often. Your Volkswagen experiences help to make this Site what it is today! jay
Thank you, Gavin. It’s my pleasure.
Thanks, I’m pulling that main jet carrier and jet from my 1967 bus tomorrow to check for chokage.