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 TM 55-1905-219-14-8
4-7.2. CARBURETOR - MAINTENANCE INSTRUCTIONS.
f. The figure below illustrates carburetor action during high speed operation of the engine. Note that the
butterfly shutter is full open to permit maximum flow of air through the mixing chamber. Velocity through the
mixing chamber at this time is comparatively high, but may be varied by re-positioning the butterfly shutter. To
obtain maximum air velocity in the area of the high speed jet, a venturi ring has been installed. The ring
consists of a funnel-like constriction in the air stream. This constriction is an abrupt curve on the input air side,
gradually tapering to a full diameter on the output side to result in maximum air velocity in the area of the high
speed jet.
g. High and slow speed jets do not function independently of each other. However, maximum vaporization
takes place at the slow speed jet only when the butterfly shutter opening is partially closed. As the butterfly
shutter is opened, vaporization increases at the high speed jet, reaching maximum at full butterfly shutter
opening. At the same time, slow speed jet vaporization is at a minimum. Therefore, the slow speed jet
functions in various degrees throughout the entire speed range of the engine, while the high speed jet remains
relatively idle when the butterfly shutter is closed for slow speed engine operation.
4-102
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