Main System (Medium Throttle Opening); Main System (Fully Open); Date Of Issue: March, 1995 - Honda Motorcycle Service Manual

Piston valve type throttle valves have a cut-out on the intake
side. The larger the cut-out, the greater the volume of air
entering and the leaner the mixture.
With a degree of opening 114-314: the fuel drawn from the
tapered section of the jet needle is regulated. The greater the
valve opening, the further the tapered jet needle rises, increas-
ing the cross sectional area for fuel passage and thus the
volume of fuel supplied. In piston type throttle valves, the jet
needle contains clip grooves in five stages (Stage 1, 2. 3, etc
counted from the top). The clip position stage number in-
creases with an increase in the degree of throttle opening,
raising the cross sectional area of fuel passage, and hence the
volume of fuel.
THROTTLE VALVE (PISTON VALVE TYPE)
:Q
?--
CUT-OUT
STAMP (indicates cut-out)
The larger the number is,
the leaner the mixture becomes.
Main system (medium throttle opening1
When the throttle valve is opened to raise the engine speed, a
greater volume of air-fuel mixture is required than for idling.
The carburetor is equipped with the main system for this pur-
pose. The degree of opening of the throttle valve is divided into
t w o stages.
With a degree of opening 118-112: the air flow in the main
bore facilitates a drawing up of the fuel from the gap between
the jet needle and needle jet (see Carburetor Theory). The
fuel is aerated by air which has entered the air bleed hole of
the needle jet holder from the main air jet.
The size of the main jet does not affect the air-fuel mixture
ratio at this stage, as the fuel flow at main jet is greater than
at the needle jet.
AIR
-
NEEDLE JET'
JET HOLDER
SMALL
LARGE
CLEARANCE* (Fuel passage
,
@CLEARANCE
- k
*
s$
I
is narrow.)
. , a & @
*@@Y
Main system (fully open)
With a degree of throttle opening of 112- fully open, the ven-
turi bore diameter and mass flow of air become maximum. At
this time the volume of fuel drawn from the gap between the
needle jet and jet needle becomes too great and exceeds the
flow volume of the main jet.
When the clearance between the needle jet and jet needle is
too great, the fuel flow is regulated by the main jet t o prevent
an overly rich fuel-air mixture.
Date of issue: March, 1995
8-6
$2
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MOTOR CO..LTD.