Try this, pull the carb, but don't replace anything. Just give it a good cleaning with carb cleaner. Don't pull the float or float valve either, just check the operation. Make sure it goes up and down (in and out of the port where fuel enters) and isn't stuck. Clean out and blow carb cleaner through all the little holes and re-assemble. If there is a clog that is causing it, you probably will fix it. If it's the diaphragm, you won't do any harm. Don't change any adjustments (idle, fuel air both hi and lo). You could also have a clog in the hi fuel air jet, but you can do all of this without any fiddling with those adjustments.
Just pay careful attention when you dis-assemble. Which way the front plate goes on, the rear plate, which way the gasket is facing and on the diaphragm, which way it is installed (there is a front and back side to that gasket.
You should be able to reassemble the carb and it will seal with the old gaskets as long as you don't tear one taking it apart.