any joy with your Bike Ian?

well I still think its either the front plug or something with the fueling, does seem to be running rich...

I've had no time to have a proper look tho, will just have to put up with it for the time being

The colour of your plugs will tell you whats going on...Assuming it's a mixture problem.

Stuck choke is another favourite with this bike. I doubt that replacing the stock can with the richer jetting would make it run that badly, or make that big a dent in the fuel economy. Another thought, if the carb float sticks and floods the bowl, is there an overflow pipe or does it just pour into the motor?

well Nekkid seems to be having a similar problem

http://forums.sv650.org/viewtopic.php?t=14302

Hello Ian,
Always worth checking the black foam under the tank. If is is anyway loose, it can be sucked down(especially under sudden hard acceleration) & acts like a choke over the air intake.
Also, don't just inspect visually, make sure all of the foam is firmly stuck to the tank underside by pinching & pulling(not too hard of course!)
George

more than likely your flooding the thing with the airkit

ie too much air and gas when you crank the throttle

the standard box is a flow restrictor which you now havent got

also as a flow restrictor is the end pipe ( can) and the 3 rd restrictor is the downpipes but these will flow more than the rear can handle anyway