BRP 2995 Johnson - Carburetor Operation

FUEL SYSTEM
CARBURETOR OPERATION
Low-Mid speed
i- i::::::::::::~::::: ::: ::::: : :-: r y------------------------------~--- - --- -------------- ---------------~- :
1. Pi/at jet
2. Pi/at air jet
3. Pilot outlet
4. Bypass port #1
5. Pilot screw
I~----'- ¢ ~
o @
¢ ~ ::~~~~~~~-
y AIR \
... FUEL +AIR (MIXTURE) (2) n J1e!--,-~_--::;:;--""
"FUEL ~
CD
As the throttle valve is opened gradually, air flowing through the throttle bore increases in proportion to 6
the valve opening angle. At this time, because fuel mixture jets from the bypass port #2 and those
upstream
successively, the optimum mixture ratio (A/F) is maintained, raising engine speed smoothly.
Mid-High Speed
1. Main jet
2. Main air jet
3. Main nozzle
(2) ,
<;=; AIR ¢ k ,, ~4 :: 1 1: t- -::::L----= -+ =---l
.. FUEL+AIR (MIXTURE) m~
@ II rr------:::?'
... FUEL CD-I"I-----I
When the throttle valve opens further and engine speed rises, fuel passes through the main jet and
enters the main
nozzle, in which it is mixed with air supplied from the main air jet before sprayed into the
main bore.
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