Pilot System; Slide Cutaway (1/8-3/8 Throttle); Jet Needle/ Needle Jet 3/8--3/4 Throttle - Polaris SCRAMBLER 50 Service Manual

PILOT SYSTEM

(Idle-3/8 THROTTLE)
The pilot system's main function is to meter fuel at idle
and low speed driving. Though its main function is to
supply fuel at low speed, it does feed fuel continuously
throughout the entire operating range.
Fuel for the pilot jet is drawn from the float bowl, mixed
with air regulated by the air screw, and delivered to the
engine through the pilot outlet.
The mixture is regulated to some degree by adjusting
the air screw. When the air screw is closed, the fuel
mixture is made richer as the amount of air is reduced.
When the air screw is opened, the mixture is made
more lean as the amount of air is increased.
General Carburetor Representation
Main Jet
3.8
Throttle Valve
Throttle Stop
(Idle Speed)
Screw
By-
pass
Pilot Outlet
Air Screw
Pilot Jet
FUEL SYSTEM/CARBURETION
SLIDE CUTAWAY
(1/8-3/8 Throttle)
Throttle valve cutaway effect is most noticeable at 1/4
throttle opening.
pre-determined for a given engine to maintain a 14:1
air/fuel ratio at part throttle. A steep angle would
indicate a fairly lean mixture because there is less
resistance to air flow. A flat angle would provide a
much richer mixture because there is more resistance
to air flow.
The venturi shape can be adjusted for each engine's
breathing characteristics by using a different valve
cutaway angle. A number will be stamped into the
bottom of the valve (e.g. 2.5) indicating the size of the
cutaway. The higher the number, the steeper the
angle.
General Carburetor Representation
Cutaway Angle
Air Jet
Air Box
Side
JET NEEDLE/NEEDLE JET
(3/8-3/4 THROTTLE)
The jet needle and needle jet have the most effect
between 3/8 and 3/4 throttle opening. Some mixture
adjustment can be accomplished by changing the
location of the "E" clip on the needle. Moving the clip
down raises the needle in the jet passage and richens
the mixture. Moving the clip up lowers the needle in
the jet passage and leans the mixture. Letter and
number codes are stamped into the needle and the jet
indicating sizes and tapers of each.
The amount of cutaway is
Throttle Valve
Jet Needle
By-pass
Pilot Outlet
Engine
Side
Pilot Jet
Needle Jet
Main Jet