I also had this problem about a year ago (657A carbs with 110 mains / 40 pilot and needle 4th from top) ...sooty plugs, poor idle and stalling when puling away from standstill once the engine was hot (fine when cold).
Wasted a lot of time and effort adjusting pilot screw and needle positions; finally went for #38 jets and what a difference!! - all running great with good response from closed throttle and clean/tan plugs.
Incidentally, now need full choke for starting regardless of ambient temp, but switch off completely soon after the engine has fired up and maintain the revs using the throttle until it warms up to steady tickover.
I buy genuine Keihin Jets at reasonable prices from allensperformance.co.uk