[Gaz64]

If you rev it to 3000 rpm, does it have close to the same airflow as the other cylinders?

Leakdown test by itself is a good secondary test after a compression test.

A misfiring cylinder will not alter it's own airflow reading, it will affect another cylinder in the firing order.

Example: one could have a broken inlet rocker arm, leakdown of 3%, and rough running due to no intake stroke.

Swap 2 carbs around, you may have a twisted throttle shaft.