11-1
CARBURETOR
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CARBURETOR
OVERVIEW
Overview ..................................................................................page 11-1
Identifying carburetor items ..................................................page 11-3
Carburetor check sheet ..........................................................page 11-7
CARBURETOR
This simple device has one purpose: atomize fuel and air into a combustible ratio.
When working with the carburetor, always keep in mind the following:
Most carburetor problems are from contamination (dirt, rust, sludge, etc). If the engine will not start while fuel is present
at carburetor bore (venturi) and the spark plug is wet, your problem is usually elsewhere as long as fuel is fresh.
The idle circuit has the smallest ori
fi
ces (jets) and passages in the carburetor and is therefore the most prone to clogging.
Air leaks in the intake track, blown gaskets or a cracked insulator block will cause problems when the pressure di
ff
erential
(engine vacuum) is highest. This occurs when the throttle blade is closed and the engine is in the idle position. The
pressure di
ff
erential begins to decrease when the throttle begins to open, and is lowest when the throttle bore is wide
open. For this reason, intake air leaks have minimal e
ff
ect on high-speed operation.
NEEDLE AND SEAT (FLOAT VALVE)
This device has one job: to control the amount of fuel in the
fl
oat bowl reservoir. If the
fl
oat bowl is over
fl
owing, there is a
problem with the
fl
oat valve/
fl
oat circuit. Dirt or wear of the
fl
oat valve is most likely.
FLOAT
The fuel level when properly set keeps a stable amount of fuel available for delivery. A higher
fl
oat level will cause a richer
mixture throughout the range; this would be a small amount of change and hard to detect in most cases.
Note: After repairing a carb over
fl
ow problem, always change the engine oil. Fuel will have over
fl
owed and run into the
crankcase, severely diluting the oil. The
fl
oat valve seat and hinge assembly are not replaceable.
IDLE (PILOT) CIRCUIT
This manual does not cover every aspect of carbu-
retion. The Honda service manual covers carburetion
in greater detail and can be purchased from J&J.
For GX-270, 340-240 engines use #61Z5f00E3
For GX-160 and 200 engines use #50300690.