If memory serves me correctly, you have a BV18 carb. The float should have a bendable tab on it. If you bend it up slightly, the float won't need to raise as far to shut off the fuel. When I adjust the float on a carb like that, I attach a piece of hose to the fuel inlet so I can blow into it and make sure the float is working the way I want it to. Hold the carb upright, like it would be installed in the motor, with the bowl off. With the float hanging down, you should be able to blow into the hose. As you slowly raise the float to the horizontal position, you shouldn't be able to blow into the hose no matter how hard you try. Don't use compressed air. Just blow into it.
