This does seem like a good place to poke at since the problem is with fuel flow... The carb as a priming button...i have held it in until fuel flooded over the float bowl into the mixing chamber, but still nothing. I have used this model carburator (4 of them!) on several bikes over the years and find them to be beyond extremely reliable - instant start ups every time. Similar to your line of reasoning I thought the needle wasnt reaching down into the bowl but when i pull the throttle assembly apart there IS ample fuel coating the needle like there should be. Its almost like there is a blockage somehow.