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Mr A


KYH

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Greg is correct on all accounts. The flapper is activates by intake vacuum, and that is controlled by an electrical solenoid in front of the airbox. The ECU fires the solenoid to open or close the flapper. At idle, in gear, clutch pulled in, the flapper is held open. When the clutch lever is released, the flapper is then held closed until rpms exceed 5500 rpm at which point is opens again.

 

The thing that will determine whether the flapper is open or closed in gear at idle is the clutch switch. If this is making intermittent contact, the ECU will cycle the solenoid on/off and you get the crackling or buzzing sound from the solenoid. The intermittent clutch switch contact can be due to dirty contacts in the microswitch, you can try to clean those with contact cleaner or just replace the switch (it's cheap and a common part). 

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