Operation Of Systems; Float System; Starting System - Honda Motorcycle Service Manual

FUEL SYSTEM
Operation of systems
The carburetor is comprised of a starting system which uses
either a choke valve or starting enrichment valve, a float
system for fuel supply, and slow and main jet systems, etc.
The fuel supply system varies with the degree of throttle open-
ina and reaulates fuel according to a slow system at low throt-
JET
tie o~eninns (throttle opening: fully closed
to
114 open),
I
(
JET NEEDLE (Straisht section,
,
-
"
medium throttle openings (opening: 118-3141, the main
I
svstnrn's
i e t
needle is used to reaulate the fuel. The straiaht
SLOW JET and AIR SCREW
. - ~ ~
~~ ~~
" "
section of the jet needle regulates at 118- 112, and the jet nee-
dle clip position or jet needle tapered section diameter
regulates at 114-3/4. When the throttle is fully open (actually
L
I
FUII 118 114 112 3/4
Full
closed open
a range of 112- fully open) the fuel is regulated by the main jet
L
of the main system.
Float system
The float chamber holds a constant level of fuel so the engine
is provided with a stable supply of the required air-fuel
mixture.
As fuel is consumed and the level in the chamber falls, the
float and float valve are lowered and the chamber is
immediately refilled to a specified level. A rise in fuel level
causes the float and its vaive to rise, the valve contacts the
vaive seat and the fuel supply is cut off. This operation repeats
while the engine runs.
The float valve contains a spring which lightly depresses the
valve so that it does not become dislodged from the seat by
vibration when the vehicle is running.
To keep the inside of the float chamber at atmospheric
pressure, there is a connection to the outside o f the carburetor
known as the air vent passage.
An overflow tube is provided to drain off any excess fuel to the
outside of the carburetor, should the valve and seat become
separated due to the intrusion of dirt or other foreign matter.
Starting system
To improve starting when the engine is cold and the fuel is not
sufficiently gaseous, the carburetor is equipped with either a
choke or starting enrichment valve to enrich the mixture.
<Choke system>
A valve is fitted to the air cleaner side of the carburetor. The
valve is shut down during starting to reduce the mass flow of
air and create an increase in negative pressure in the main
bore. The resulting mixture is rich, having a proportionally low
volume of air.
The choke valve is provided with a relief mechanism which en-
sures the optimum opening of the valve under conditions of
negative pressure above a certain level, thus preventing the
supply of an over-rich mixture to the engine.
Lf
VALVE PIN
Date of Issue: March, 1995
8-4
o
HONDA MOTOR CO..LTD.