MG Car Repair: 1967 mg-b, vacuum leak, vacuum advance

Question
i installed a weber carb. conversion kit,i cannot get the engine to idle smooth the rpm is 750 motor jerks and I don't get much change when adjusting the fuel mixture screw, i changed the idle jets to a smaller orface to no avail.motor runs great at 1200 rpm and above.got answers?

Answer
Hi Chuck,
If it idled good with the SUs and don't now. you may have a vacuum leak or something is wrong with the idle circuit in the Weber. What did you do about the vacuum advance connection?
Try this, when the engine is warmed up and idling at 750 slowly start restricting the amount of air going into the intake with your hand. If at any time as you start restricting the air supply, the engine smoothes out or speeds up, you have a vacuum leak or you are too lean on the mixture.
Howard