Ok then if your compression is even like that start over then with the WSM to balance the carbs. It sounds like one carb is shutting off at idle and they are way out of balance. There could still be a vacuum leak but if you have ruled that out with brake clean, visual inspection etc then check balance and mixture back and forth until it idles smoothly. Start with setting the carb butterflies in sync, there is an adjuster to do that on the linkage at the front of the carbs, reference the WSM for instructions. Once they are set, you want to balance the carbs using the air volume screws. Quick easy method to check balance is to bend up some wire into a 'P' with a very long top part that will then fit down into the piston dashpot when the dampers are removed. Set them pointing at each other as close as you can get them. It will look like someone holding two divining rods looking for underground water. If you google "using an SU tool kit" you will find instructions on using the SU factory tool but you can just use some wire to do the same thing. The SU tool kit has aluminum tubes that the P wires fit into, but you can just bend a long wire with a U on the end to fit snugly down into the dashpot with the legs pointing towards each other. Get them so they point exactly at each other at stop, then start the engine and idle, if the carbs are balanced they will point exactly at each other when at idle. I suspect they will be way off, so then adjust air volume screws and see if you can get them to point at each other at idle. After adjusting the volume screws to get them to point at each other, you will have to check mixture on both and adjust if necessary, then balance again and adjust mixture again until the rods point exactly to each other at stop and idle. You check mixture by lifting the dashpot piston a tiny bit using the spring loaded pin on one side of the carb that pushes up to lift the piston from the bottom. Let it idle 15 seconds, lift the pin until you feel it touch the piston (you will see the rod start to rise) then lift a further 1/32nd of an inch. If the engine idle speed goes up and stays up, you turn the mixture screw anti clockwise a bit. Rev engine a little, let idle another 15 seconds and try again. If the idle speed drops and stays down when you lift the piston, you turn the mixture screw clockwise a bit. Turn the mixture screws no more that 1/8 or less at a time. You are trying to get to where the rods point to each other at all rpm's, and the idle speed will go up just a tiny bit then immediately drop back to what it was when you lift the pin.
Also pull the float bowl vent hoses off so the weakener system is disabled while you are adjusting just in case it is malfunctioning and interfering with the running. Doubtful from what you have described, but it's possible.
