running lumpy

[YamFazFan]

In higher revs, I.e above 5000rpm it seems a lot less noticeable. When the bike is cold and at lower revs its like a tractor. The first header pipe gets warm but not unbearably hot to touch

Yep that's just how my Fazer was running.

Once I got past approx. 5000rpm it pulled like a train as per usual, but was lumpy and hesitant again below that figure and also on start-up.

Down pipe number 3 was noticeably cooler after a ride and that was where the problem lay, with carb number 3.

The garage did an ultrasonic clean of the carbs and it felt like a new bike afterwards

Apparently the issue was caused by degraded/stale fuel mucking the carb/s up.

I did try a fuel system cleaner additive prior to the carb removal but it made no difference, although I used a Motul product and not the STP one which Frosties, darrsi and others on here have reported good results with.