BRP Johnson J25R4SUR - Low-MID Speed; MID-High Speed

FUEL SYSTEM
CARBURETOR OPERATION
105
6
Low-Mid Speed
As the throttle valve is opened gradually, air flowing through the throttle bore increases in proportion to
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
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.
1 Pilot jet
2 Pilot air jet
3 Pilot outlet
4 Bypass port
5 Pilot screw
6 Throttle valve
AIR
FUEL+AIR (MIXTURE)
FUEL
1. Main jet
2. Main air jet
3. Main nozzle
AIR
FUEL+AIR (MIXTURE)
FUEL