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Carburetor Adjustment & Tuning Tips
128 Adjustments for Competition
Carburetor Adjustment & Tuning Tips
The carburetor used on your CRF will seldom
experience trouble with the standard settings under
average load, and average climatic and barometric
conditions. However, to fine-tune the engine’s
power output, the carburetor may require specific
adjustments for competition use.
However, in order to comply with emission
regulations, we recommend that you make no
carburetor changes unless you use your CRF for
competition only.
Cold Start Circuit
A very rich mixture must be delivered to the
cylinder when a 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.
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.
Carburetor Components
(1) choke knob (4) throttle valve
(2) starter jet (5) orifice
(3) air passage
(1)
(5)
(2)
(4)
(3)
(1) hot start valve
(2) main bore
(3) hot start air passage
(2)
(1)
(3)
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