i have seen this problem on several occasions on this model and it has always been a problem with the catyltic converter in the exhaust coming loose and blocking the gas flow .what i have done in the past is cut the pipe right in half with a hack saw and weld it back together after taking the cat out first of course it will be loose in there and rattling around. its about 5cm accross and 3cm high and shaped like a fruit pastile but not as tasty :D
adam bike doctor(of milton keynes motorcycle centre)
November 2010