OK, finally got my 89 GS 500 trackbike together and took it out on some WOT runs.  1-3 runs great all the way to redline.  In 4-5 however at around 6krpm it just wont pull past that.  Valves are done, havent done a throttle body sync yet.  No vacuum petcock, full gravity system, single 1/4" line with 1 fuel filter. 

Current jetting is

Pilot:  40
Main:  125
Needle:  Shimmed 1 #4 washer

Air mixture screws set 3 turns out

Intake/exhaust stock

Any ideas?  Maybe the main jet is too small to handle load at that range?

Obligatory pic

Do a carb sync before anything else, my 93 has the exact same jets, washer, air screw settings as yours and after the carb sync it was a whole different bike. Before it would struggle just to get to 75mph now if I am not careful I can see triple digits (OK well 110 maybe)  Although I still see a 5-6k stumble, once its past that it pulls strong. Do the sync and let us know how it goes.

Yep I was going to do a sync this week, just figured id pick peoples brains before hand.  The jetting seems to work well for alot of people that are stock.