You may know all of this, but just in case....your carb has three basic circuits - idle, cruise/mid-range, and wide-open. Your accelerator pump bridges the transition from idle to mid-range, or from idle to WOT giving a shot of raw fuel into the venturi to prevent stumble (going lean on the change in air flow). For the three screws you mention, idle speed is easy - adjust it to the speed you want or as specified for your engine. The other two are idle jets, which meter the amount of fuel into the airstream during idle. At idle speed, the old school adjustment is to turn in a screw until you note an rpm decrease (lean falloff point), then turn that screw out, counting the turns until you reach a rpm decrease (rich falloff point), and set the screw at the mid-point between the two. If you don't see rich/lean falloff points it probably indicates that you're leaking internally, and you need to put a kit in it. If you're running rich in mid-range and/or WOT those fuel circuits are adjusted with changing out main jets and/or metering rods, depending on the carb. Some can be done easier than others. What type of carb are you working with, and where are you seeing the it too rich?

My answer is very basic stuff, and I'm not trying to infer you're not way more of a carb guy than I am.