Bought a Mc18 recenly, someone is having a good look at it, including power valves and carbs but when it is done in about a week I probably need to do a plug chop. I've already done the splice. It was idling uneven with the left pipe puffing way less than the right and the left also letting out a lot of black when riding a while, am trying to make the call for the airbox, any advise still available for mc18?