559 / 612
Cutaway Drawing
Use the cutaway drawing (above) to learn about the inner
workings of the Super BN carburetor. Starting with the fuel pump, fuel
enters through the fuel inlet, being drawn in by the engine’s pulse acting
on the pump diaphragm. The fuel passes through a series of check
valves and then the fuel required by the engine passes through a fuel
ilter. Excess fuel is diverted through a restricter and then back to the fuel
tank via the fuel return. The purpose of the fuel restricter is to act as a
fuel pressure regulator for the fuel pump.
After the fuel passes through the ilter it goes directly to the
needle valve assembly and then into the chamber. Fuel low into
the fuel chamber is controlled by the regulator diaphragm, arm spring,
arm and vent to the atmosphere. These components, along with the
needle valve, make u to the regulator portion of the Super BN. As you
will learn, the Super BN is part carburetor and part fuel regulator. The
regulator portion controls fuel low at lower speeds, idle to 1/4 throttle,
and the carburetor portion controls fuel low from about 1/4 throttle to full
throttle.
At idle, fuel is drawn through the low speed jet to the low
speed jet to the speed outlet, via the low speed adjuster, and to the
bypass holes. The low speed adjuster controls fuel low for a
smooth idle and initial throttle response. As the throttle valve is
opened from the idle position, the bypass holes are increasingly
exposed to the air low. Their function is to help the carburetor
“transition” from low speed to high speed operation. The size of the
low speed jet directly affects fuel low through the bypass holes for
low speed performance. the other function affecting low speed per-
formance is the regulator portion of the BN. the regulator portion
can be tuned by changing the arm spring tension of the size of the
needle valve, or both. More of that later.
As the Super BN transition to its high speed fuel circuit,
at about 3/8 throttle, fuel is drawn through the check valve is to
prevent the low speed circuit from sucking in air through the high
speed jet passes through the inner venturi then into the enine.
The high speed adjuster controls the maximum amount of fuel low
for full throttle performance from about 3/4 throttle opening.
Super BN
Internal Components
551