18 hp B&S Carb problem

[eightwheeler]

i have an 18 hp B&S flat twin and it runs great untill you rev it to the max then let off, the motor just shuts down, so i purchased a rebuild kit and am now wondering about the bottom Jet/Screw by the manifold, does anyone know what that one does and how many turns in it should be?

Thanks again

[Jeff t-boss]

If you are referring to the one with the plactic cap on it, that is the main mixture screw. The plastic cap is a limiter that only allows you to adjust to a set parameter. You will have to take it off during your rebuild. I never put them back on when I'm done. After your rebuild, your initial setting is to turn the screw all the way in and LIGHTLY seat it. Then back it out 1 1/2 turns. Start the motor and let it warm for a few minutes. then run the rpms to about 2500 and hold. Turn the screw in till motor sarts to miss. Still holding the rpms, turn the screw out till the motor misses again. Then turn the screw 1/2 way between the two points.