I have a 1974 Johnson 2 hp which will start but only run for 4 seconds or so and then stop. I replaced the coil, points, plug, condenser, and rebuilt the carburetor. It has good spark, compression of 80 psi, and the fuel is flowing well to the carburetor. I have taken the carb apart several times but it seems to be clean as a whistle and the float and needle are operating properly. I thought the problem was perhaps defective reeds, but I have cleaned them with a very soft brush. If I hold themk up to the light I can see a VERY SMALL crack of light coming through. The lower unit is operating properly. What am I missing??? Thank you.