Make sure the air valve dashpot [ right side, rear of carb ] is in good cond. When old, the internal rubber goes hard causes strange problems. Buy a new one if in doubt.
To adjust: engine idling, there should be 1/16 - 1/10" of freeplay when you gently push down the rear of the AV. This takes up the slack in the dashpot link arm. Bend the arm to get this dimension. Make sure the arm/AV does not hang up in it's travel.
