Weird sound diagnosis

[SS109]

Can anyone tell me what I'm hearing with the pitch of my exhaust changing? I have never encountered this before. Engine wasn't overheated, coolant is good, and the plug looks good (no detonation). Anyone have a clue or been through this?

https://youtu.be/YiTibRu2dos?si=STnHlkHmBtP3J5uY

 

[gasgasman]

Power valve flapper hanging.

 

[Jacob 'Berg]

+1. Is it making far less power at low rpm when the exhaust note changes?

Time to clean the power valve and/or replace the bearings.

 

[SS109]

Thanks guys. I just did the top end 55 hours ago. Everything was fully cleaned and inspected. Even replaced one of the bearings on the powervalves. Oh well.

 

[Wbdisco]

Let us know after you dig into it, I?m curious as well.