My mate changed the belts and air filter and spark plugs and now it runs really rough and misses and jerks then comes good then after a while it will do it again when cruising at 80 or 100 it will run good then start to run rough and miss and jerks and then comes good for a while then does it all over again after a while when going through the gears it's really rough and jerks and misses until you get the revs up its worse when it's cold than when it's warm