2000 xp surging at full throttle

[azsxr]

So I got this 2000 xp that I just got running. I rebuilt the carbs and changed the fuel lines.it ran pretty good pulled alright up to 6850. After a few min it would only get 6000-6200 and sound like it was surging but didn’t feel like it was surging as far as I could tell.
I opened the high adjusters a 1/4 turn out and no change.
Any ideas