Just been tinkering with the zip and its running a 75 main jet? It has a silent pro (not my choice at all), modded airbox and all restrictors removed (including the lil brass carb plate). Noticed it has a 75 main jet? hock: Plug is absolubtly spot on though, cant work it out? Surely 75 should be overkill, im assuming the airbox mod is whats balancing that out?
I wouldn't have thought so, if the plugs fine i wouldn't touch it, if anything was blowing you would know by sound/power decrease. my speedfight 50 has a 76 jet in it as well with just an exhaust. I know it's not the same bike but you get the idea?