hi guys I have a 2000 thunderace and when I took it out of the shed the other morning it seemed to have developed a misfire . very lumpy at low revs and not wanting to pick up unless given a handful and stinking of petrol I have replaced the standard exhaust with a stubby race can and thought this could have caused the problem but after replacing the standard exhaust yhe misfire continues could it be as simple as a plug off or something more serious