Unfortunately near the end of the day the bike decided to only run on 2 cylinders and wouldn't rev past 9k so I nursed her into the pits. Popped her on the trailer and called it a day. I wasn't overly concerned at the time about the nature of the problem as during the middle run I'd ran out of fuel (queue the walk of shame, with the bike, up the pitlane
) I figured that some crap from the tank had made its way into the carbs and they were blocked. Having the time and weather all this week I've been doing a few needed fixes and cleaned out the carbs (they were fine). So I start her up. As always full choke press button and she starts instantly. However the bike doesn't sound right and something doesn't feel right so I switch her off and take a step back to ponder whats going on. After a few minutes I convice myself that I'm just being a tart and fire her up again. Nope somethings clearly not right. I popped my hand over the back of the exhaust (something I do, I've no idea why) and noticed there was nothing comming out! 
well a gnats fart was about all that was comming out. Quickly turned her off and had a look at the end can. Its a mess 
. The baffles have rotted away inside and I guess its pretty much blocked. I removed the end can and gave it a shake.. It was like a childs rattle. Its in the corner awaiting a saw to see just how bad it is. I popped an end can from my old thundercat on (just to keep the noise down) and fired her up and she idled and sounded much better 
MY concern is that could I have done any damage to the engine as I guess this all happened througout the trackday and the backpressure must have got pretty severe. When it went to 2 cylinders on the track there was an audible bang... or at least I felt like there was - I was pretty focused on the track. The bike starts and idles fine with the thundercat micron exhaust so I'm hoping i've not done anyting seriously bad. Any thoughts?
Also, providing I've not totally screwed my engine, is it worth looking for aftermarket exhausts and rejetting or is it a whole world of hurt? I've had a very quick look on ebay and there is plenty of different cans just wondering wether to keep it standard or have a play.
Over to you my learned friends
I figured that it would most likely be fine but as its not road legal I couldn't go for a quick run to make sure. It would probably run like a dog with the thundercat exhaust on anyway. I've read through the carb setting up procedure a few times (it was invaluble when I first got the bike