Demon Fuel Systems 4402020VE - Manual (Page 13)

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will open. The lower the number, the more the vacuum has to drop for the valve to open. When the
engine is under a big load, it produces decreased manifold vacuum along with an increased demand
for fuel. When the manifold vacuum is less than the rating on the power valve, it opens and allows
extra fuel to enter the main circuit of the metering block. It is a good idea to have a power valve rating
that is lower in number than the vacuum produced by the engine at idle. Road Demons are supplied
with a power valve blow-out protection valve in the baseplate.
Figure 18
Main Body
The main body’s unique top shape increases the air flow capacity over standard carburetor designs.
The accelerator pump squirter and the air bleed bosses have been moved back to further improve
flow characteristics. These changes have an effect on the overall performance of the carburetor.
Figure 19
Air Bleeds
The air bleeds, located in the upper portion of the main body between the wall and the venturi, shape
the fuel curve by helping to control when the idle and main circuits start. The four (4) idle bleeds are
located closest to the air cleaner ring, while the four (4) high speed bleeds are found on either side of
the squirter bosses. A larger bleed can be used to slow down, or delay, the related circuit, and vice-
versa for a smaller bleed. As with the emulsion bleeds, tuning with the air bleeds should be done only
by someone with a deep understanding of carburetion to prevent a poorly operating carburetor.
Squirters
The exit orifice diameter of either of the squirter controls the duration of the pump shot. The smaller
the diameter, the longer it will take for the complete volume of the pump to discharge. A larger
diameter discharges the
pump’s volume quickly. This is assuming no changes in pump cams.