I'm a slack bastard!
Sorry for this long arse post
I got my mate who has NSR/RS experience to give me a hand... as I am a numb nuts when it comes to engines.
I finally got the airbox lid off (ok I didn't do it, my firend did) but the bolt would still not come out... lucky my mate had a spare which he didn't need and saw pity on me to kindly donate it
Thanks Karl!
We got the carbs off and removed the float bowl from the right carb and cleaned it out. There was some gunk, so we thought that we had found the problem and preceeded to put the carbs back and connect the fuel to test it, but it was still not right.
We weren't sure what size the jets were, but the bike was running fine before our winter break (Jun, Jul, Aug), so we decided not to mess with them yet.
We then swapped the reed cages around. Found out I have dual stage reeds in there
... but they weren't the cause either.
We then tested the compression difference between both cylinders. Top: 120 - Lower: 115-118
K was fearing the worst as he had once experienced these symptoms before on his NSR and it turned out to be a collapsed crank bearing
... I also told him that Andy had said it might be the rings, so we proceeded to remove the lower barrell to check the rings and crank bearing.
He noticed some signs of detonation on the head of the piston and some light scoring down the sides (I tried taking some photos but the fuckin camera wouldn't focus properly
). The crank was ok though... Thank God for that 
The walls of the barrell seemed ok, but we noticed some pitting on the cylinder head due to the detonation. I guess there's no excuse not to do the centre plug head conversion now
We haven't taken the top barrell off yet, but is it worthwhile rebuilding the top cylinder if I am doing the lower? Or can I get away with just doing the lower?
This is oh so much fun... NOT
Thanks again guys for the advice.
_________________
Jerry Lai
NSR250 [MC21SP]