1200GSA exhaust flap

[(RIP) Bin Ridin]

Hi,
For curiosity, I took photos of the flappy thing today. I got the closed shot just after turning on the key, more like an exhaust brake. Feck.
Tried to watch it operating while riding, never caught it closed or closing, only full open.
Puzzled, what does it do?
Bin

 

[Deleted account 240901001]

Puzzled, what does it do?
Bin

Isn’t it obvious? It’s to stop mice crawling in and adjusting your valve clearances in the night…..

 

[Ravenbyrne]

They open and close as you open and close the accelerator thus controlling the air/fuel mixture. I THINK

....and don't you know that it's very dangerous to ride your bike while looking down.

 

[Wapping]

If it operates the same way as a conventional 'power valve' it fools the engine into thinking that the exhaust pipe is of a variable length.

'Shorter' when you want maximum 'umph' / acceleration, 'longer' when you want stable power / cruising. It does this by restricting the diameter of the exhaust pipe, altering the pressure wave / back pressure. 'Narrow' looks to the engine like a shorter pipe etc. etc.

http://en.wikipedia.org/wiki/4-stroke_power_valve_system

 

[Ravenbyrne]

If it operates the same way as a conventional 'power valve' it fools the engine into thinking that the exhaust pipe is of a variable length.

'Shorter' when you want maximum 'umph' / acceleration, 'longer' when you want stable power / cruising. It does this by restricting the diameter of the exhaust pipe, altering the pressure wave / back pressure. 'Narrow' looks to the engine like a shorter pipe etc. etc.

http://en.wikipedia.org/wiki/4-stroke_power_valve_system

yeah............. that's what I was trying to say

 

[Engineer]

It is what makes the 2010 GS lovelier to ride at low speed and gives it a noticeable fatter gob of low speed torque compared to the older 1200s. I can ride in first gear with my hand off the throttle and it bimbles along at tickover without needing any clutch slip; on the flat it is happy doing this in second gear too.

 

[tunnie]

It is what makes the 2010 GS lovelier to ride at low speed and gives it a noticeable fatter gob of low speed torque compared to the older 1200s. I can ride in first gear with my hand off the throttle and it bimbles along at tickover without needing any clutch slip; on the flat it is happy doing this in second gear too.

Take hand off throttle in mine and it starts braking heavily

Couple of times i wanted to coast, don't feel comfortable doing it with clutch in

 

[Engineer]

Take hand off throttle in mine and it starts braking heavily

Couple of times i wanted to coast, don't feel comfortable doing it with clutch in

No No No! it will trickle along at a constant speed at tick-over without juddering

 

[Account removed]

If it operates the same way as a conventional 'power valve' it fools the engine into thinking that the exhaust pipe is of a variable length.

'Shorter' when you want maximum 'umph' / acceleration, 'longer' when you want stable power / cruising. It does this by restricting the diameter of the exhaust pipe, altering the pressure wave / back pressure. 'Narrow' looks to the engine like a shorter pipe etc. etc.

http://en.wikipedia.org/wiki/4-stroke_power_valve_system

+1 0n that, they still use the valve on the full race Akrapovic system.

Check out the torque on the Akrapovic web site for just the end can on standard headers and then look at the 09.

 

[(RIP) Bin Ridin]

Would this flap be effective on managing the power curve, despite being downstream of the cat? I have a recollection it is there to moderate noise for EU drive-by test, but would love to get a functional description.
Bike is loosening up and getting a bit more perky, 2000kms.

 

[veefour]

Take hand off throttle in mine and it starts braking heavily

Couple of times i wanted to coast, don't feel comfortable doing it with clutch in

+1

In higher gears there's so much engine braking I sometimes think it's stalled - apart from when I had the cam sensor problem and it did stall it locked up the rear

 

[Engineer]

Would this flap be effective on managing the power curve, despite being downstream of the cat? I have a recollection it is there to moderate noise for EU drive-by test, but would love to get a functional description.
Bike is loosening up and getting a bit more perky, 2000kms.

Yes - why not?, the exhaust gases still manage to get through to the outside world quite effectively despite the slight restriction of the cat - if they didn't the engine simply wouldn't work.