With the lid inverted (upside down), the floats will shut the needles and no airflow will happen.
Lift the floats at that point and they should weep one at time.
You can also have the lid with the floats hanging down and both needle and seats will be open, lifting one float at time will shut the needle, but difficult to determine if they are leaking with one float still open, don't lift them up too hard, you'll alter the float adjustment AND damage the needle.
Best bet is to take out the float hinge pins, take out the needles, take out the seats, check the inlet passageway for debris, blowout the passageway, reassemble, check floats are straight and not fouling the main body, check float level and drop as per manual.
How about fuel pressure? Have you measured this?
Is the aircleaner lid far enough away from the bowl vents?