Brake changes exhaust note

[CamaroMan79]

I noticed  on my agility 125 today while ideling at a stop light that when i press in the left brake handle(rear) it changes the sound of the exhaust. Anyone else notice this on their scooter?

Also, I noticed that when my scooter is warming up from a cold start, the idle goes up and down. Is this normal? It has even died a few times while warming up.

[Hoolander2]

Yes, I think the revs going up and down during warm up is normal.  My Xciting does it.  And sometimes nearly stalls.

When I apply either brake while stopped, my mirrors, handlebars, and windshield all vibrate more.     I think it's because that takes away the ability of the tire/wheel assembly to absorb some vibration. 

Do you think you're hearing more of a vibration than the exaust? 

[CamaroMan79]

Hard to tell.

[Whisper]

  TOTALLY Normal - You'll experience that on any bike/scooter where the engine has a direct connect to the rear axle.
 
  Basically, you are clamping down on the rear wheel - not allowing it to move or vibrate, even a little.  AND pressurizing the brake line, making it much stiffer.  When you do that, the vibration from the thumper will vibrate the whole vehicle a bit.  Frequency, reverberation, etc of the vibration will change as the whole unit is engaged in the vibration - exhaust not may change as the engine moves differently.

   
 

[Portland Steve]

Hmmm, Whisper has an interesting theory,
My guess is that the belt is turning just a bit at idle.  When you hit the rear break it stops the belt, causing the engine to do a bit more work, thus changing the exhaust note.
Could be similar to when you kill the clutch on a motorbike and the engine changes tone, only in reverse.

[TechGuy]

Hmmm, Whisper has an interesting theory,
My guess is that the belt is turning just a bit at idle.  When you hit the rear break it stops the belt, causing the engine to do a bit more work, thus changing the exhaust note.
Could be similar to when you kill the clutch on a motorbike and the engine changes tone, only in reverse.

The belt is always moving... it's just when you are below a certain rev point and stopped, the clutch shoes release and you don't move forward. When the engine is running, the front variator sheaves/pulleys are moving..so the belt moves and that moves the rear sheaves. Its the presence or absence of the clutches connection to the rear wheels drive shaft via the clutch bell that determines if you are moving or not.

Try releasing the rear brake while keeping the front brake on to hold you still.  It will change the feeling/sound.