Re: 37 will turn over but not fire.

Posted by Owen_Dyneto On 2009/11/6 10:15:54

Sanford, the float or fuel level is the single-most important adjustment to make when redoing a carburetor. Think of it this way - though a bit over-simplistic. You want a relatively constant air/fuel mixture over a range of rpms: properly set, the fuel level in the bowl (established by the needle & seat adjustment) is just a tad below the tip of the main jet. As the air flow induced by the piston suction passes thru the venturi in the carburetor, it creates a vacuum in the region of the tip of the main jet and "pulls" gasoline into the air stream, atomizing it in the process.

If you set the fuel bowl level too high (above the jet tip), you'd have a constant flow of gasoline off the jet not controlled by the volume of air flow, hence you'd run rich. Also, even with the throttle plates closed and no air flow thru the venturi, you'd still be pumping gasoline into the engine, with no or insufficient air to make a combustible mixture.

If you set it too low, the vacuum created in the venturi would be unable to draw the specified volume of gasoline, and the result would be a lean mixture.

Take the time, set it accurately!