Fuel consumption

[John H]

Not everyone gets really good mpg!! Since the lock-down period, our '29 chummy has been using more fuel than (I think) it should. On the 120 mile run to Moreton in Marsh in July, we appear to have averaged 32mpg, cruising at 40-ish on roads that are not all that hilly either. The brakes are not binding, and the car's performance is fine, but fuel consumption is heavy and the spark plugs always look very black and sooty. Also, it hesitates when pulling away from junctions, something which it never used to do. The carburettor is a bronze FZ updraught. The float level looks good and all the jets are clear and standard size (measured with proper jet drills). The needle valve doesn't appear to leak. The engine has good compressions, the valve clearances are right, the ignition system is in good order. It starts and idles well, responding correctly to the slow running adjustment. My thought is whether there is an air hole or passageway in the carburettor that has become blocked, making the mixture go rich? Dunno? It always used to do 40+ mpg on long runs, so what has changed?

Any thoughts?