your carb will have two adjustment screws,one is for mixture,ie,fuel adjustment,the other will adjust tickover,my geuss is youve adjusted the mixture screw and now have either set it to lean or to rich to run.....your tickover adjustment screw will adjust somewhere on the throttle mechanism,find the end of the throttle cable then follow through the throttle mechanism until you find a screw that adjusts against that mechanism,this is your tickover adjustment.....the other screw is normally set in to a slight recess,but may not be,regardless,if youve found another screw that effects the tickover then this will actually be your mixture screw,by rule of thumb,if you screw that screw right in til its tight,but not to tight else youll snap the needle on the end,once its done right up then undo it 3-4 turns,once you hit 3 turns then turn very very slowly until the engine is running even,ie,the revs are settled and not going up and down by themselves,by rule of thumb,3 and a half turns is the factory setting from new and should get your engine running nice,once youve done the mixture then go back and adjust the tickover............where the brakes are concerned,from reading your post im geussing youve dismantled the rear calipers,these are threaded inside and are also sprung,the threaded shaft goes right through to the rear where it comes into contact with the hand brake mechanism,you should find that so long as the piston goes back into its sleve then the threaded part will rethread itself once you apply the brakes,its basically like a self adjuster and as you push the piston back in you should feel the piston trying to turn very slightly,this is because its come into contact with the threaded part,basically,so long as you can refit the calipers with the pads and the brake is not binding or stuck on,then the caliper will sort the rest out for itself.........master cylinder is an easy job,but take my advice and buy a new clutch master as well,thats if you go down this road,then just take the whole pedal assembly out and change them on your bench,then refit....easy life!...ps,i have a pedal assembly,with both working cylynders knocking about that you can have for free if you wanted it and decide to go down this road ok
