Also in addition to Den’s comments, remove the overflow pipe and make sure that the very fine bleed hole behind it into the manifold is clear.
If you want to try a different Solex Copy Carb let me know and I’ll post you mine. It was running OK whilst I had the original overhauled.
I suspect yours is an original if the car has been off the road that long, it will have solex cast into it (copies don’t) and will have a serial number stamped into the top by the fuel inlet, copies don’t.