Honda CRF250R 2005, Owner'S Manual

Page: 120 / 164

Carburetor Adjustments & Tuning Tips
116
Adjustments for Competition
Accelerator Pump Circuit
The accelerator pump circuit operates when the
throttle is opened. As the throttle valve (1) opens,
the pump rod (2) depress the diaphragm (3). At
this time, the inlet check valve (4) is shut
resulting in a sharp increase in pressure in the
pump chamber (5). The outlet check valve (6)
then opens, supplying fuel to the main bore via
the accelerator nozzle (7).
(1) throttle valve (5) pump chamber
(2) pump rod (6) outlet check valve
(3) diaphragm (7) accelerator nozzle
(4) inlet check valve
Slow Circuit
Fuel is metered by the slow jet (1) and mixed
with air from the air passage (2). The mixture
enters the venturi through the bypass (3) and
pilot outlet (4) that has been metered by the pilot
screw (5).
(1) slow jet (4) pilot outlet
(2) air passage (5) pilot screw
(3) bypass
Main Circuit
Fuel is metered by the main jet (1), jet needle (2)
and needle jet (3). It is then mixed with air
coming from the air jet (4) and enters the venturi
past the needle jet.
Baffle Plate
The baffle plate (5) prevents foaming of fuel or
abnormal fuel level around the main jet.
Float Bowl
The float (6) and float valve (7) operate to
maintain a constant level of fuel in the float
bowl.
(1) main jet (5) baffle plate
(2) jet needle (6) float
(3) needle jet (7) float valve
(4) air jet
(3)
2
(1)
(7)
(6)
(2)
(5)
(4)
(3)
(2)
(1)
(5)
(4)
(6)
(4)
(2)
(7)
(5)
(1)
(3)