Thanks Busman, there is a little play on the throttle butterfly shaft on all the carbs I’ve tried but nothing that I would deem to be excessive. I’ll try the WD40 trick tonight and report back.
Wristpin, Paul at Meetens said he stripped it apart, sonic cleaned it an then rebuilt it with new parts where needed. I have since found an old damaged seal on the cover plate to the idle jets from inside the float chamber. I suspect it could be drawing fuel up into to idle jets from the float chamber so I’ve managed to order a new o’ring seal 9.6mm od x 6.7mm id to rule this out, took some finding as it’s a really unusual size!