I had this problem and there can be two different problems. First and the easiest test is to check the fuel level in the front bowl. Take the screw out the side of the bowl, when the engine is shut off. If fuel comes out of the bowl you need to change the float level. The fuel level should just be at the bottom of the screw hole. The float level can be changed by loosening the top screw on the bowl and then adjusting the level with the nut. The second problem can be the power valve. The front power valve may not be sealing correctly or be broken. I would try to take of the metering block and make sure the power valve is tight. Mine was loose one time and the idle was completely rich. There needs to be a good seal or the power valve will leak and too much fuel will enter the engine. Also check to make sure the power valve is not stuck open. You can also use a vacuum gauge on it to test the opening point.