Got ya. Now makes more sense. Id start by checking all exhaust bolts are tight, and flanges tight on the cylinders. Make sure the exhaust chambers arnt hitting the cool head, the motor vibrates a good bit so if there isnt enough room it will hit the chambers. If still there pull the head and make sure you didnt drop something in there(seems silly but shit happens) if still there pull clutch cover and make sure you installed every thing correctly. No primary gear play, clutch basket and hub timed correctly, clutch springs torqued properly ect ect.... Also did you get the right fuel for the dome change? Could be detonation aswell