The two little screws are for holding in the jet block and to locate the slide throttle.
Over fueling is caused by the needle and seat not shutting off ,usually fuel leaks out the overflow hole in the carby.
Also over fueling can occur if the float setting is incorrect ,it should be 3/16 setting in the pic below.
Another cause is when the float has a hole and fills with fuel and no longer floats ,you can usually shake the float and hear fuel in the float. Just make sure the float can move up and down easily.
I'm not sure how much cleaning has been done but a lot of people just remove the fuel bowl and clean the parts they can get to but your better off completely dismantling the carby ,taking main jet out and the jet block and cleaning out all the orifices.
Don't remove the lever retaining drive screw on the float lever but on some of these the primer button needs removing and cleaning.
There is a hole in the side at the top of the jet block that lines up with a hole in the carby body when assembled,( this compensating port should be cleaned)
once the jet block is removed the float lever can be turned sideways to remove the needle and clean and inspect condition also the fuel hose connection on the carby body should be unscrewed and cleaned.
Sometimes there is crud in the tank, tap and fuel hose and you clean the carby put it back on, runs well for a short time then crud gets back in the carby so it's best to clean out the fuel tank and tap and if you are using an old rubber fuel hose replace it as old rubber perishes leaving small particles of rubber in the carby.
With the images they are expanded when double left clicked once opened or download to computer and open.(easier to read)
