First I would check that the right carb has free fuel flow by opening the float bowl screw and watching the fuel run out of the bowl with the petcock open. You'll want a clear container to catch the gas so you can look for dirt and water. Then I'd check both squirrel condoms for dry rot and insure the manifold rubber is intact and is in fact right side up and oriented correctly front to back. Have you had the top off the carb? Because the diaphragm can be hard to re-seat sometimes and that's another source of frustration. What else have you tried?
