It’s a 1993 yamaha out board 250 horse power with 6 carburators . The passage way from the fuel inlet to the?

it’s a 1993 yamaha out board 250 horse power with 6 carburators . The passage way from the fuel inlet to the needle valve in the float bowl is clogged. They have been soaking in carb. Solvent for days and have been blown with compressed air to no avail. It doesn’t seem to be a varnish {old gas turns it it} issue. How to clean this passage is the real question