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11-2
CARBURETOR
Speci
fi
cations and prices subject to change without notice. Download latest update to this manual on-line.
To provide fuel for idling (when throttle blade is closed) a special circuit feeds just above the main circuit and routes fuel
out of the
fl
oat bowl, through the pilot jet, mixes it with air from the idle air corrector and circulates it around the throttle
blade to provide a fuel/air mixture so the engine will continue to run when blade is closed. Fuel is pushed out of the
fl
oat
bowl and up the idle circuit by a pressure di
ff
erential. The idle air corrector introduces a calibrated amount of air into
the circuit; this air/fuel mixture passes through the adjustable idle mixture screw jet and discharges into the intake track
beyond the throttle blade.
NOTE:
The pilot jet is the smallest ori
fi
ce in the carb. It can be removed and cleaned without removing or disassembling
the carburetor. Remove the idle stop screw and gently pry out the pilot jet assembly (it is held in by an “O” ring). Make sure
the fuel strainer and
fl
oat bowl are clear of debris before restarting the engine. The pilot jet is a replaceable part, however,
no alternate sizes are available.
With the pilot jet removed, other blockage can be cleaned by removing the idle mixture adjustment screw and using a
fi
ne
tipped air nozzle to blow out back through the passages. An aerosol can of carburetor cleaner with a spray tip can be used
to clean and trace out various carb circuits.
TRANSITION CIRCUIT
This part of the idle circuit splits o
ff
ahead of the idle mixture screw and feeds a series of very small parts that open just
as the throttle blade begins to move. This provides an extra amount of fuel for a smooth transition from idle circuit to the
main circuit. If the engine hesitates just o
ff
the idle on smooth acceleration, you could have fuel restriction in this area.
MAIN CIRCUIT
From approximately 1/8” of throttle to fully open, the main circuit
fl
ows fuel out of the
fl
oat bowl through the main
fuel jet, up the main air fuel nozzle to the venturi. The fuel delivery carburetor circuits used in this application have two
requirements: fuel and air in calibrated amounts. This provides the air/fuel ratio the engine requires. When cleaning
passageways and/or troubleshooting, it is always necessary to clear the air passage, as well as the fuel passage. The holes
in the side of the nozzle start out small at the bottom and get larger toward the top. These holes introduce air into the
main circuit and also prevent fuel from siphoning into the engine intake.
NOTE: The main circuit controls engine fuel from 1/8” of open to full open. Any carburetor problems below that range
cannot be caused by the main circuit.
CHOKE
A cold engine requires a richer air/fuel ratio to run until the engine combustion chamber temperatures are optimal. To
accomplish this, available air is reduced by “choking” o
ff
available air to the engine. A simple
fl
ap restricting the bore does
this job.
NOTE:
The original Honda/Keihin carburetor uses a plastic composite choke shaft and lever system. This has proven not
to withstand the rigors of concession go-kart use, therefore, J&J builds an all-metal replacement for this system. Part #
2090017METAL.
THROTTLE BLADE/LEVER SYSTEM
This part is not replaceable, however, throttle plate screws can loosen slightly and cause idling problems with bad
fi
t in the
carb bore. Seat the blade and snug the screws; these screws are “peened” over on the end and are nearly impossible to
remove. Extended shaft wear can cause an air leak around the throttle blade and cause erratic and/or high idle.
NOTE:
Any carb jet can build up with varnish or other material that will not be dislodged with carburetor cleaner or an air
blast. Always hold them up to the light and verify that there is a nice, clean, round hole.
K&N LIFETIME FILTERS
Part#
Description
Price
SP-2748
Filter, Air GX240, 270 K&N
$39.98
SP-2747
Filter, Air GX160, 200 K&N
$39.98
99-5000C
Filter, K&N Oil/Cleaner Kit
$16.00
99-0516C
Filter, K&N Filtercharger Oil 12oz Aerosol
$10.44