From what you say, it seems like either the first filter before the pump is clogged, or enough crud has gotten into the float bowl(s) and clogged flow to the jet. In your test with the jug, did you still have both filters inline? I'd take the filters out of the circuit, just to make certain that they aren't the culprit. If still no flow, I'd pull the float bowl covers and have a look.

IIRC, without removing the carb bodies from the manifold, you can remove the float bowls with the jet still attached by loosening the through bolt that holds the float bowl to the carb, and while the jet is still attached to the float bowl, carefully pulling the jet down out of the jet centering housing. And then make sure that those are clear (compressed air). Probably advisable to first remove the bell and piston to avoid scratching the needle when removing the jet.