This car belongs to a client who hired me to bring it out of 4 years improperly stored in a chicken barn. Got the car out of the barn this past weekend. He plans on flying to Ontario from Alberta and driving the car back when I'm done addressing everything that's wrong with it, and put insurance on it so I can drive it and find any issues before the trip.

Work done so far on the engine is new plugs/wires/cap and rotor, drain fuel tank of stale fuel, adjust valves and an oil change. Have new fuel and air filters on the way.

After sorting out the braking issues, we took it out on a 200km round trip. The car ran flawlessly, silky smooth power delivery, smooth idle, great acceleration. This morning I got in it and set off on my 5 km drive to work, and at the first stoplight it started bucking and surging and just running terrible at a stop. Would run awful, clear up for a second, run a bit worse, run awful again, run a bit better, etc. acceleration does not seem to be affected.

Had it in the shop tonight to turn the brake rotors and decided to look down the carb. At idle, one barrel is getting a constant supply of fuel, while the other is getting none at all. I don't know which one is normal, but judging by the smell of the exhaust I'd say it's overfueling. I'm guessing a chunk of crud in the fuel system has come loose and is now in the carb, but I have zero experience with this particular carb or multi- barrel carbs in general. Below is a video looking down the carb at idle, you can see the difference in fuel delivery. Any input on the issue would be greatly appreciated!

This is how it's running today...

At the front of the carb, just below the float bowl, will be found two idle cut-off solenoid valves, each angling inwards. Carefully pull off the electrical connectors from each valve, and clean the pins and sockets. Corrosion accumulates over time and eventually raises the contact resistance enough to cause one valve to close. Just outboard of each valve is an idle mixture screw. Exercising them, i.e., 1/4 turn in, 1/4 turn out, may also help.

Take this step first, to insure that it is not the problem. You may very well be correct that there is an internal dirt problem, but this step is easy.

Did anyone else notice that the carb looks very much like the Rochester carbs used by GM in the 70s and 80s?
Great carb. Biggest problem with them was the float sinking which raises the fuel level in the bowl. Also, ethanol did a lot damage if allowed to sit for long periods of time. I think you said it had been sitting for 4 years.
I don't want to get started on ethanol and the damage it can do, but I am afraid it may apply here.

Paul

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84 500 SEL (307,xxx miles)

I've heard if quadrajets being retrofitted , but it's not really something I wanted to get into on a customers car.

I pulled off the electrical connectors and found little to no corrosion, contact cleaned and brushed everything out anyways. Also worked the idle adjustment screws, neither helped. Pulled the plugs and cleaned them, which have me enough time to limp the car up to the auto plaza my gf works in, where one if the old guys said he was familiar with these cars and the Solex.

Two days later I get a phone call, the vacuumn diaphragm for the secondaries isn't working that great, and the secondaries are sticking open, causing fuel to just pour in. Metering valves are also sticking. Bottom line is it's looking like the carbs going to have to be rebuilt.