I had a similar problem after i installed a freak kit and rejetted. Bike used to break down like it was running out of fuel in top gear at about 3500 - 4000 revs. After days of eliminating things i discovered that the needle jet holder and pilot jet had some holes partially blocked with crap. Cleaned them and blew them out and now all is fine. i then removed the tiny filter at the T junction and fitted an inline glass fuel filter at the petcock. Was surprised that something so minor made such a difference to performance.
