UK Car Repair: Carb/choke for Zenith/Syromberg =77MGB, mg engines, stromberg carb

Question
I own a 1977 MGB with a single Stromberg Carb. The choke is has got me in knots. I've tried several different chokes and they all are running too rich, to the point of killing the engine. Can you explain the theory of how this choke works? Maybe I could fix it, but when I ask anyone who claims to know something about MG engines, they simply say the choke wears out and you have to replace it!!!

Answer
The choke doesn't wear out, the needle and jet can but it is unusual.  This is a water activated assembly, it is possibly just stuck open.  Inside the water activated unit is a coil spring and orifice plate, as the engine temp increases the spring tightens and rotates the orifice plate closing the fuel passage and lowering the idle speed. You could strip it and see but, before doing so, contact Burlem Services in Salisbury, they can provide you with the service parts.  Another alternative is to convert the choke to a pull cable available from any of the Jag/MG/Triumph specialists.