My 1960 BSA A7 has started to misbehave at small throttle openings. This happens going from a closed throttle and during the first say 1/4 to 1/2 inch of "twist" if that makes sense. Bike splutters, misfires etc. Will conk out if I stop at a junction on shut throttle. Absolutely fine with throttle open any wider, in fact it's really sweet. This happens irrespective of whether the bike is hot or cold and on or off choke. Running monobloc carb bought new couple years ago from SRM, who incidentally set the bike up ignition and carburration wise on their rolling road dyno this time last year. It's been great up to now. Any ideas where to start looking? I'm a bit of a newbie with tinkering with classics, I've had the bike for several years but my knowledge is very limited. I always used to call on my big brother for these kind of things as he grew up with them, but sadly he passed away last month unexpectedly. Any help would be greatly appreciated!! Thanks,
Al