The last thing you write is very important
Only 8 minutes on a tank is not long enough. I had the same problem with the OS Speed XZB. Only got 7.30 on a tank, after getting the OS back to the standard idle gap and setting HSN and LSN I got runtimes of 10min + on the same track!
You have to make sure that the idle gap is between 0.5mm an 0.8mm, then tune op your HSN Needle and then the LSN needle.