Yamaha YZF-R1P Service Manual page 29

Pressure regulator
It regulates the fuel pressure that is applied to the injectors that are provided in the cylinders in order
to maintain a constant pressure difference with the pressure in the intake manifold.
The fuel that is delivered by the fuel pump fills the fuel chamber through the fuel inlet of the regulator
and exerts pressure on the diaphragm in the direction for opening the valve.
A spring that is provided in the spring chamber exerts pressure on the diaphragm in the direction for
closing the valve, in contrast to the pressure of the fuel. Thus, the valve cannot open unless the fuel
pressure overcomes the spring force.
An intake vacuum is applied to the spring chamber via a pipe. When the pressure of the fuel exceeds
the sum of the intake vacuum and the spring force, the valve that is integrated with the diaphragm
opens, allowing the fuel to return from the fuel outlet to the fuel tank, via the fuel return hose.
As a result, because the intake vacuum fluctuates in accordance with the changes in the operating
conditions in contrast to the constant volume of fuel supplied by the pump, the valve opening/clos-
ing pressure also changes to regulate the return fuel volume. Thus, the difference between the fuel
pressure and the intake manifold pressure remains constant at a prescribed pressure.
1 Spring chamber
2 Spring
3 Diaphragm
4 Fuel inlet
5 Fuel return
6 Fuel chamber
1 - 8
FEATURES
7 Valve
8 Intake manifold vac-
uum pressure
GEN
INFO
È Spring pressure
É Fuel pressure
Ê Vacuum pressure