Should be 3/8 id hose. I use a in- line one way check valve between bulb and engine as that eliminates the sometimes iffy bulbs. The next thing I would do is open up the idle screws,one at a time starting with the top carb. Maybe turn it "two hours" at a time. Using the clock as a template. The transition circuit is poor on these engines so the idle screw will let a bit more fuel into the carbs to get her up on a plane.