The Zenith 28, or 228 uses a check ball in the fuel intake.
Does the check ball need to be there? Yes, it does, along with the check weight.
The important thing is that the check ball can't come out of the hole. The suction of the accelerator pump coming up and the weight of the fuel lifts the check ball up. If the check ball comes out of the hole and rolls around the bottom, the whole process won't work. The check weight on top of the ball is there to hold the check ball down when accelerating. The check weight can be made from 1/8" welding rod, cut so that there is 1/16" clearance from the top. This is so that the check ball can lift up. The check weight weighs about 1 gram.