XT Newbie here, hello everybody!

I recently bought an XT660R 2006 with a lot of goodies already fitted. It has PC, Speedo healer, K&N filter and Metal Mule exhaust. Also a lot of acerbis goodies and small cosmetic mods.

The bike ran and is still running fine but something happened last week when riding home from work. I overtook a couple of cars when suddenly I felt a momentary loss of power and the sound from the bike was a bit different, a bit quieter. This happened during the overtake which made it a bit creepy.

Now it feels like I don't have 100% of the power I had before. Based on my butt dyno, there's like 90% left of what I had in the beginning. It runs OK, I can take it on the highway no problem but the peak power is missing.

Also, the final twist of the handle doesn't give the desired response. Is there something simple I should check, something that can shake loose or such? Thankful for any help! Cheers!