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Your guide to check and properly adjust a
motorcycle's air/fuel mixture.
PRE-ADJUSTMENT CHECK
LIST
-
Before
making any fuel system adjustments, check all tune-up related
adjustments.
-
Idle
RPM should be set at the factory specified speed. The engine must
be at full operating temperature.
-
Properly secure the motorcycle to a lift.
CARBURETOR ADJUSTMENT
PROCEDURE
Idle Adjustment Procedure
-
At
idle, adjust the idle mixture screw(s) until CO in the exhaust
pipe is between 2-4%.
-
If CO
cannot be set above 2%, increase the slow/pilot jet(s) one size.
-
If CO
cannot be set below 4%, decrease the slow/pilot jet(s) one size.
-
With
CO between 2-4%, using a tachometer, adjust the idle mixture
screw(s) until idle RPM reaches a maximum (around 3.0% CO).
-
Adjust
the idle speed screw so idle RPM is at the factory specs.
-
Record
the CO level at idle RPM.
Cruise Check
-
While
in neutral, accelerate to mid range (1/3 of maximum RPM) and
hold for 20-30 seconds until CO stabilizes.
-
At
this RPM, CO should be 1/4 to 1/2 of the CO at idle.
-
If CO
is less than 1/4 of the idle results, the engine is too lean.
Install a larger slow/pilot jet(s) or raise the needle(s) one
step.
-
If CO
is more than 1/2 of the idle CO, the engine is too rich. Install
a smaller slow/pilot jet(s) or lower the needle(s) one step.
FUEL
INJECTION ADJUSTMENT PROCEDURE
Many fuel
injected bikes have an idle adjustment which should be set between
1-3% CO. After market fuel injection modules are available for bikes
which have no adjustments. These units typically have adjustments
for idle, mid, and high RPM ranges. Again, CO levels should be
between 1-3% for each of these ranges.
These CO levels are general limits where most engines operate well.
The best source of these levels is the factory specifications for
each particular engine, fuel system and exhaust combination. Always
refer to the OEM's specifications for CO exhaust emissions.
© Copyright 2001 Blanke Industries, Inc. All
rights reserved.
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