Make sure the carb overflow hose is not plugged and it shouldn't leak into the air box. As for the screws that hold the carb bowl on, make sure your screw driver fits the screws real tight. Different tips and even different brands with the same tips are different sometimes. If one won't fit good, then try another brand. Before you try to loosen them, put the screw driver on the screw and give it a sharp tap with a hammer or rubber mallet. Obviously, the carb will need to be off to do this. A lot of times this will jar the screw and help to loosen it. If you do strip the head out, cut a groove accross the center of it with a dremel and cut off wheel and use a flat or slotted screw driver to get it out. If you don't have a dremel, you can sometimes use a hack saw, but it is a little harder to do, but can be done. I always take them off to work on them anyway, because it is a lot easier, for me anyway. It sounds like your float is just stuck. Take it out and pull your needle valve out and make sure it is clean and make sure the hole where it goes is clean and don't have any debris in it. Better to blow it out with an air hose if you can. Be careful when you pull the float out that the needle valve don't fall out as it is usually attached to the float with a little wire clip. While you have the float out, if it is plastic or metal, make sure it don't have a tiny hole in it. Sometimes you can shake it and listen for gas to slosh around inside it if it has a hole. I doubt that it will be metal, because they haven't used metal or brass in carbs in a long time. Sometimes they will be made of some type of solid plastic or material of some sort. Hope this helps. Good luck with the repair.