Austin Big Seven starting problem

[john williams]

There is a little confusion here with carburettor terminology. The "Choke" is the reduction in diameter in the main inlet section of the "carb". On Zenith carbs this choke size is a fixed diameter. The cold starting device, commonly, but incorrectly called the "choke", is actually the "strangler valve". This is the flap on the inlet of the "carb" which is operated by pulling out the "cold start" cable. Again incorrectly called the choke cable. On early Zenith "carbs" the the cold start flap was fixed solidly to the operating lever. This caused a problem when the engine started, as the engine could not draw enough air to form a mixture as the throttle is opened. Common parlance "Over Choking". On later "carbs" the cold start flap valve is spring loaded, it closes in the same way as the early "carbs when the cable is operated, but the spring loading, allows it to open  automatically when the throttle is opened. It sometimes happens that the spring closing of the cold start "strangler valve" fails. Thus the cable and strangler valve lever operate normally, but the strangler valve flap sticks in the open position. Easily cure with penetrating fluid on the strangler valve shaft.  Check that with the cold start cable fully out, the strangler valve is fully closed. Then apply finger pressure to the flap valve, it should open easily without moving the cable operating lever. If it is difficult to move, it would seem you have the early type of "carb" which is prone to "over choking". However, even with these early carbs, the engine usually starts easily, but will not rev freely, and eventually the engine stalls as the spark plugs become soaked. I hope there is enough information to guide you to a successful solving of your problem, but at the very least it should clarify some of the carburettor terminology.