Fuel leak at fuel bowls

I recently rebuilt a quickfuel 580 4 barrel carb for my 318. Yesterday I installed the carb and started the engine. It runs great, but after I shut it off and checked for leaks I noticed a small amount of gas where the fuel inlet fittings screw into the bowls. The inlet fittings are AN style, I installed them with new white nylon washers supplied in the rebuild kit, I screwed them in almost all the way by hand and then snugged them up with a wrench. Any idea of why they would still leak?

Thanks.