problem running

[stuart fishleigh]

hi folks. my old man has a Norton rotary classic. it starts up fine but when its at running temp it coughs black smoke on tic-over.i have cleaned the carbs, fitted new spark plugs, no change!common sense would say over fueling, blocked idle jets.have also checked diaphragm in fuel tap and vacuum pipe.any ideas?cheers stu.

[Interpol2471]

Have you checked the o rings on the choke enrichening device as these crack allowing extra fuel into the inlet? I think Richard posted some pictures some time ago on the removal, if not it's very easy