Operational Description - Honda CB350 Repair Manual

With the exception of SL350 K—models,
the carburetors used on 350/360 Hondas
are of the constant—velocity type. The
$L350 K—models are equipped with two
direct—control type carburetors. The dif—
ferent types can be easily identified by
the throttle cable connection. In the
direct—control type carburetor, the throt—
tle cable enters the carburetor top; while
in the constant—velocity type (CV) carbu—
retor, the throttle cable connects to a
lever at the side. Both types are manufac—
tured by Keihin.
The following description of the opera—
tional theory of the carburetor may be of
some aid in pinpointing carburetor mal—
functions.
Operational Description
The function of the carburetor is to
meter an fuel—air mixture into the com—
bustion chamber in amounts which vary
according to engine speed. The ratio of
air—to—fuel is usually maintained at 15 to 1
(by weight) at atmospheric pressure at
sea level (14.7 psi).
Basically, a carburetor consists of a
float bowl, a fuel nozzle, and a venturi
Float assembly
1. Float
2. Needle seat
3. Needle
4. Float tang
5. Fuel inlet passage
tube. Fuel from the gas tank flows into
the float bowl! in amounts monitored by
the float. The float is connected to a nee—
dle, and when the fuel reaches a preset
level, the float presses the needle into its
seat, stopping the fuel flow. Then, as the
gas is consumed by the engine, the float
drops proportionally to allow more fuel to
enter the bowl. In actual operation, the
float rarely closes offthe fuel supply com—
pletely (except when the engine is shut
off or for several moments at idle), but
reaches a balance in which the amount of
fuel consumed matches that entering the
float bowl.