To eliminate the float bowl as a possible problem area, you could remove the side of the float bowl (it's held in by the main jet and an O ring around the outside) then turn on the fuel and see how well it flows (leaving the float in place). Next, lift the float gently and see if it shuts off. Work it up and down a couple of times to see if it is consistent. As Bob said, it may just be stuck shut. If it is a large body of crud upstream of the seat, you will get slow fuel flow when the float is right down. Remember to put the float bowl side panel back on with the same orientation it had originally.
