I know I have answered this question before – In the 1950s when these classics were build, it was thought that the percentage of the fuel that could bypass the high speed needle valve through this route was so small that it could easily be compensated for with a fractional turn of the adjustment knob. Since this percentage grew as the outboards demand for fuel decreased, the smaller motors required that the small gap at the junction of the upper and lower carburetor castings be sealed. This changed with the introduction of the fixed jet carburetors. This reduced the number of complaints from people with misadjusted carburetors while increasing the numbers of motors damaged from running too lean. For those who trusted themselves more than they trusted the engineers, a kit was offered for the high speed needle valve. These were a necessity for motors used at differing altitudes. . . 😎
