Classic Cycles Technical Resources
43
When the kick starter lever is depressed with the throttle valve closed, air induction is generated behind
the throttle valve by the engine suction. This condition is similar to that created when the choke of a
conventional carburetor is fully closed. As the throttle valve is closed, air is inhaled only through the
starter air channel. Strong air induction is generated at the fuel jet located at the narrow starter plunger.
Fuel in the float chamber is metered by the starter jet and moves up the emulsion tube. Air is inhaled from
the wall of the tube and a rich mixture of air and gasoline is made. When secondary air is added to this
mixture, a correct rich mixture for starting a cold engine is inhaled into the engine through the nozzle
located behind the main bore.
NOTE: It is most important that the throttle valve be left closed when starting the engine. If it is not, the
rich gasoline/air mixture will be leaned out. Too, the raising of the throttle valve hampers the inhalation of
this correct mixture by taking away the vacuum ordinarily created when the kick starter is depressed.
(2) Slow channel (mainly for idling)
The suction stroke of the piston induces air at the pilot outlet of the carburetor so that gasoline is metered
through the pilot jet and air is drawn through the pilot air hole and metered by the air adjusting screw. The
gasoline and air make a rich fuel mixture which jets from the pilot outlet into the main bore where it mixes
with a small amount of air and is supplied to the engine, along with a correct amount of oil injected into the
intake between the carburetor and the engine.
(3) Main Channel (mainly for medium and high speeds)
Air entering the carburetor from the air cleaner passes under the throttle valve and is inhaled into the
engine as the main air flow. Induction is created at the needle jet by this main air flow and gasoline in the
float chamber is metered by the main jet and enters the needle jet. This gasoline passes through the gap
between the needle jet and jet needle and flows into the main bore of the carburetor. The gap between the
needle jet and the jet needle is controlled by the throttle grip, so that when it is opened the gap increases
and the flow of gasoline increases and when it is closed the gap decreases and the flow of gasoline also
decreases.
To Next Page
Loading...
