Honda CRF250R 2005, Owner'S Manual

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Carburetor Adjustments & Tuning Tips
Adjustments for Competition
115
The carburetor on your CRF should perform
suitably with the standard recommended settings
under average load, climatic, and barometric
conditions. However, to fine tune the engine’s
power output, the carburetor may require
adjustments for specific competition needs.
Optional main jets and slow jets are available for
your CRF. See your Honda dealer.
Any engine or airbox modifications or the use of
an aftermarket exhaust system may require
jetting changes.
Carburetor Components
Cold Start Circuit
A very rich mixture must be delivered to the
cylinder when cold engine is being started. When
the choke knob (1) is pulled out, fuel is metered
by the starter jet (2) and is mixed with air from
the air passage (3) (located above the throttle
valve (4)) to provide a rich mixture for starting.
The mixture discharges through the orifice (5)
into the cylinder.
(1) choke knob (4) throttle valve
(2) starter jet (5) orifice
(3) air passage
Hot Start Circuit
A lean mixture must be delivered to the cylinder
when a hot engine is being started. When the hot
start lever is pulled back, the hot start valve (1)
opens, allowing air to be supplied to the main
bore (2) through the hot start air passage (3). This
extra air enters the air-fuel mixture from the slow
circuit resulting in a lean condition.
(1) hot start valve
(2) main bore
(3) hot start air passage
3
(1)
(5)
(2)
(4)
(3)
(2)
(1)
(3)
(cont’d)