Suzuki DF150 Service Manual page 90

ENGINE CONTROL SYSTEM 3-31
• HIGH SPEED RANGE
HIGH SPEED
Shut off valve opened
When the engine speed is above the preset value (*), the ECM
generates a signal to turn the VSV OFF, and vacuum is no
longer applied to the depression chamber.
Without vacuum the shut off valve return spring returns and
holds the valve in its normal open position.
In this operating mode, intake air is supplied to the engine
through the high speed intake tract only.
This enlarges the intake tract volume, improves intake inertia
and efficiency, which increases the engines output power.
Air flow