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The flap is normaly open when idle, by spring pressure action.
When the engine is running, a depression exists inside the injector body. A hose is connected on the right-hand injector, it goes thru a solenoid activated by the ECU and then to a vacuum controlled flap. Note the small air tank which allow some damping of the depression pulses.
Bellow 4000rpm :
• Solenoid is activated by the ECU.
• Depression is directed to the vacuum controlled flap.
• The flap closes.
• Air intake only go thru the small lateral duct.
Above 4000rpm :
• Solenoid is inactive.
• Depression is blocked.
• The flap is open.
• Air intake go thru both ducts.
The same device exists on some Honda bikes : the VFR-VTEC / FireBlade / RC45. The device is present on some cars too : Honda (VTEC / PGM-FI), BMW, Mercedes, Lotus, Ferrari, Volvo, Toyota... the list is certainly longer. It's worth noting there are various reasons invoqued about this device. Among them, the intake flap "...increase the airflow speed inside the injector ducts when the flap is closed, leading in a better cylinders efficiency at low rpm". Official Yamaha's documentation claims "improved drivability and reduced intake noise in the low speed range" for the TDM air-intake flap system.
The rider's experience is slightly different and not as positive :
• Engine's smoothess is not very effective at low rpm.
• The engine is very lazy under 2500 rpm and does not behave correctly, even for a two-cylinder bike.
• Some jerkyness appears around 4000 rpm.
• Users think that all those problems are connected to a faulty ECU or injection troubles.
This may be explained easily :
• Engine is starved of air below 4000 rpm by the closed flap.
• The flap is under the control of the ECU, which triggers it around 3500-4000 rpm.
• Flap works in an full open / full closed mode, without any progressive or smooth control.
Don't forget that an atmospheric engine will only draw as much air as it needs thru the air filter. Any device that block the airflow will introduce a perturbation.
On any computed fuel injection engine the fuel-air mixture is permanently adjusted by sensing the atmospheric pressure AND the depression that exists inside the injectors air duct.
This fuel-air mixture is always optimal, no matter the altitude level or which air-filter is in use, without requiring any manual carbs adjustment. In case the air-filter element is dusty, it will simply lower engine bhp.
Actualy the air-intake flap is required to comply with stiffer pollution & intake noise regulation (EURO2).
There are some benefits in desabling the air-intake flap :
• Better smoothess at low rpm.
• Torque increase, nice on mountain roads.
• Better, faster rpm increase, even from as low as 2000 rpm, without knocking.
• No more jerkiness around 4000 rpm.
Please note that inactivating the air-intake flap will NOT give you more bhp / top speed. Only usability will increase.
I found three different simple ways to achieve this improvement.
Quelle