This is a short video of a Yamaha DT125R showing the operation of the power valve.

The first thing you see is the power valve in the fully open position with the bike turned off.

Then the ignition is switched on and off three times to show the cleaning sequence.

When the engine is kicked over and it doesn't start the power valve goes to the fully closed position.

When the engine does start you can see the valve close and stay closed until the revs rise.

This bike starts to open the valve at about 6,000rpm, reaching full open at 8,000rpm.

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