Carb float leak
I've read of a leaking carb float causing too rich rough running. Carb heat warmed the air in the float, causing expansion, which pushed fuel out, restoring float buoyancy, and engine ran O.K. This lead to carb ice being assumed to be the problem. Cold air lead to contraction of the vapour in the float, and more fuel entered the float, until the mixture was so rich the engine lost too much power for the aircraft to remain in flight. The pilot made an off-airfield landing, blaming carb ice.
Would leaning the mixture work with a sinking carb float?