Xciting 500cc flapping noise from engine or crank or valves

[RyianKymco]

Hi All

I have a 2007 kymco Xciting 500cc, great ride and great scooter, i enjoy it tremendously.
I have a 2007 yamaha R6 too.

I had this flapping noise on the Kymco, i can start, ride at about 15km/h, once i start to increase speed, the flapping noise gets fast and louder but only takes about 5 seconds then it completely switches the engine off.
I was riding on the highway/freeway when it started.
I checked the bike even when i removed the Driven belt and on its centre stand, the same thing happened.
I have the entire bike stripped down to the crank shaft, everyting is perfect on the bike, bearings are perfect, nothing is damaged, nothing is loose, teh engine from eye view is completely perfect.

So what is or was wrong?
What was causing the flapping noise?
and how is it effecting the power and electricity on the bike?

[Ruffus]

@RyianKymco welcome here!
I would in such a case:
- METIN  box out
- leave the drive belt off
- take motorstethoscope or a long screwdriver
- listen at running motor where the noise comes from
Hard mechanical "flapping" or more hushed?
- could be a broken chainguide/ tensioner
- a faulty rotor
Please do a thorough checking and come back here for some more Qs. or feedback.
Maybe you could put this subject within XC 500 section.