Idle adjustment/settings

Hi to everyone on here, I recently bought back my 1980 Z1300 A2 UK carb model. I sold it 5 years ago with much regret but now it's back. First bought in 1990. It came back to me in pieces so I've spent a few weeks now getting it back together. I have it running but have a few carb issues. I'm looking for advice about how to set up the throttle stop screw on the top of the carbs that is actuated by the cam which is moved up and down by the choke lever. I've had the carbs off and cleaned everything scrupulously. I have a spurious rebuild kit but I haven't used it apart from changing the float bowl gaskets. I always had a problem with this bike getting it to tickover nicely without the throttle seeming to stick and the revs not dropping properly. It has always, and still does, run well if the main tickover/idle screw is backed off enough but it won't tickover like this.. my other issue is that one of the mixture/air screws on #5 carb has a damaged head and cannot be adjusted. I have all the other mixture screws turned out 3 1/2 turns as recommended by some experts. It runs OK but there is definately a bit of improvement to be had. Has anyone any experience with trying to remove a.damaged mixture screw? I balanced the carbs recently which improved things but there is a bit of popping and banging going on at tickover speed. I have routed the fuel supply from the original non vacuum type tap to the carbs with the T- piece pointing up and the fuel line running parallel around the top of the carbs. Fuel flow is good, all carb floats have been set and I get the same amount of fuel from each carb when I drain them. I have used the bike for 30 years with this issue and it never really bothered me but it would be nice to maybe sort it..