GENUINE Blur 150, Service Manual

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MAIN SYSTEM
As the throttle valve is opened, engine speed rises and negative pressure in the venturi A
increases. This causes the piston valve to move upward.
The fuel in the float chamber is metered by the main jet . The metered fuel enters the needle
jet , mixes with the air admitted through the main air jet and forms an emulsion.
The emulsified fuel then passes through the clearance between the needle jet and jet needle
and is discharged into the venturi A, where it meets the main air stream being drawn by the engine.
Mixture proportioning is accomplished in the needle jet . The clearance through which the
emulsified fuel must flow ultimately depends on throttle position.