GPz 1100

Hi All
I have a GPz1100 that has been converted tocarbs which are the BS34 J model ones.
I got the bike already converted and there is a slight but annoying flat spot at 5.5k to 6k. I took the carbs off to check the jetting and the main jet is at 144. The pilot jets are blanked off. The needle is set to the bottom indentation so is at iots richest setting.

I have been advised (in the UK) to go to 130 mains but that seems very small to me, what do you guys think?
TIA
Mark
PS Also posted on WG website (sorry, getting desparate!)

here are my Specs
Gpz1100b1 motor 1170 cc, 3mm over size
laser racing exhaust,
Mikuni bs34mm carbs by WG Carbs,
1 and a half turns out.
Main Jet #142.5
Pilot Jet #40,
K and n air filters, (pods)

hope it helps