Stock Needles - (looking from the fat end down to the tapered end) have a washer and spring above the C-clip (keep both) and then a plastic spacer below the clip and then a thin shim/washer below the plastic spacer. Read more. The difference between the Stock PMS screw and the Old Style MaxMix screws are how fast they taper to a point. The reason is, mechanically synchronizing your carburetors doesn't necessarily synchronize the vacuum created in the venturi, which is what really matters: equal amounts of gas and air entering each cylinder at the same time. // -->