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I've read in a lot of places that the Solex 34PICT-3 carburetor (stock on my 1972 Beetle cars around that same age) is fiddly to keep tuned with the stock timing. Many people take as gospel that this combination just has problems.
Well I'm now wondering about that I wonder if it's possible that the problems that are experienced with that carb is just a characteristic of the carb itself. In June, I put in a carb that I bought on ebay and cleaned out thoroughly and rebuilt. Right before I left for work and Oshkosh in July, the car started hestitating a little bit off of idle again. Over the weekend, I tried to effect a quick repair to make that better, and I think it may have done the trick.
Since my car had no hesitation with a fresh carb, then developed hesitation again, and now the simple cleaning fix got rid of the hestiation, I wonder if the hesitation reputation of that carb is mostly due to the passages getting clogged up.
Here's the scenario. Below is a diagram of the 34PICT carb with dots to show where air and fuel flow at idle (air is blue, fuel is red, air/fuel mix is purple). The throttle plate is closed. All the air that is getting to the engine is going through the bypass drilling on the right.
Here's the same sort of diagram with the throttle slightly open. When the throtle opens, there isn't enough airflow to cause the main jet to discharge fuel into the air stream. So if the idle bypass and the main jet were the only mechanisms for fuel delivery, as the throttle was opened the engine would run too lean and perhaps stumble or stop. To make up for this, there is a series of small metering holes to inject fuel into the air getting past the throttle plate as it opens. This diagram shows the flows with the throttle slighly open. There is air getting past the throttle, and the fuel is being metered by the holes near that opening.
This is taken on another 34PICT-3 carb that I have. This is taken of the engine end of the carburetor. The throttle is slightly open, and at the edge you can see the metering holes.
My theory is that the hesitation that I (and perhaps others) experience is because one or more of those holes are clogged. What I did, which seemed to have worked, was to take the top of the carb off and shoot carb/choke cleaner into the jets that go to the passages where he holes are. One is the upper of the two brass passages in the bottom half of the carb here:
The second is the jet that leads to the metering holes. In the above photo, it's the thing that looks like a hexagonal-headed brass bolt. The passage that goes down from the barrel of that jet goes to the metering holes.
If my supposition is correct, and the fault is gunk in those metering holes that will dissolve with carb cleaner, then all I have to do to fix it is to remove that jet and shoot cleaner into the port at the bottom. I'll try that if the problem recurrs. The jet is on the side of the carb where you can get at it without removing anything else. You can see the jet here, with the carb and everything re-assembled, the jet head below the automatic choke:
So the car ran fine today, no hesitation. If the hesitation comes back, I'll try this again.