Solex/Kadron carbs need 1.5 psi. Not one smidgeon more(2.5 psi is too much). That's probably your issue.
Drop the fuel pressure and replace the float valves(they are not expensive even with a full rebuild kit). If the floats are leaking, i.e. they don't float, replace. Otherwise, if they float and there is no gas inside(shake them) they're fine.
Electric pump, add auxiliary regulator. Mechanical pump, add gaskets under the pump until running pressure is correct.
FYI, this is what works from my personal experience, as in I have done this myself. This is not anecdotal internet BS.