she's running a stock filter and exhaust system, bar the end can.
The difference at night time (10 degrees cooler) is immense, pulls alot harder........... ???

I've never really noticed much difference in performance with changes in the weather (have done plenty of track days in very hot weather).

As air temperature increases power will naturally decrease because the air is less dense and vice versa.

It might be an idea to get it on a dyno during the day and night to see what's going on.

I'll do just that Cammo.... BUT another problem has popped up, i just replaced all the water pipes, thermostat rubber o-rings between the two cylinder heads, rad cap flushed everything through. When coming back from a 300km run down to Pattaya in Thailand today the bike spat a load of coolant out of the HRC expansion bottle. on returning home and parking her up on my drive, i could here she was hissing away :S
Took the fairings of pretty sharpish to see where the hell this air was coming from................ Found out that the upper most core on my upper rad (big uprated alloy rad) was leaking
So i'll have to get that sorted and see what happens with fueling afterwards, the rad being like this could be causing the issues regarding the strange jetting symptoms i'm having right now.....
The core only opens up when the engine is hot (long high rpm journeys) and closes at anything under 80 degrees, bit of a tricky bugger to hunt down this!! But finally found it! and i sure as hell hope that's the last problem this year (25 days left) lol :D