Main Fuel Systems
The carburetor’s purpose is to supply and atomize fuel and mix it in correct proportions with air that
is drawn in through the air intake. At primary throttle openings (from idle to 1/8 throttle), a small
amount of fuel is siphoned through the pilot jet by suction from the incoming air.
As the throttle is opened further, the air stream begins to siphon fuel through the main jet and needle
jet. The tapered needle increases the effective flow capacity of the needle jet as it rises with the
throttle slide, in that it occupies decreasingly less of the area of the needle jet.
In addition, the amount of cutaway in the leading edge of the throttle slide aids in controlling the
fuel/air mixture during partial throttle openings.
At full throttle, the carburetor venturi is fully open and the needle is lifted far enough to permit the
main jet to flow at full capacity.
