Nick --

Stoney's right on. The "breather box" (oil trap) under the flame trap assembly can get plugged solid. If that happens, all new parts -- flame trap, hoses, Y connection, brass fittings -- won't help.

Pull the flame arrestor off the oil trap so you can see the "stub". Start the engine, and at an idle you should see fumes coming straight up outta that stub. These are the vapors from the crankcase. No fumes (vapors, smoke) means a plugged oil trap.

The oil trap is fairly easy to unbolt from the block and remove. Be aware there's a hose connected to it (inside) that goes down to the oil pan. You don't want to yank that hose out of location, so be gently when removing the trap.