Download Honda Programmable FI

FUEL DELIVERY SYSTEM
Fuel Pressure Regulator (cont.)
To understand the fuel pressure requirements of
fuel injection systems, start by looking at the
conditions at both ends of the injector. The output
end of the injector points into an intake port. In
order to spray fuel into the intake port the
pressure on the supply end of the injector must
be greater than the intake manifold pressure.
When the engine is running, a vacuum exists in
the intake ports. This is measured in inches or
millimeters of Mercury (Hg). A normal motorcycle
idle vacuum pressure is about one inch of Hg., or
4.9 psi.
Fuel pressure is typically in the range of 32 - 50
psi. The GL1800, for example, uses a fuel
pressure of 50 psi. That is the pressure difference
between inlet port vacuum pressure and fuel
pressure as shown below. The fuel pressure is
set at a fixed amount above the inlet port vacuum
pressure. Therefore, changes in inlet port
vacuum pressure have no effect on the amount
of fuel that an injector delivers when it is opened
for a specific amount of time.
3-8
PROGRAMMED FUEL INJECTION