13-07-18, 11:56 PM
Black smoke could be oil. If the airbox is clean then it probably isn't getting in from the crankcase breather, which makes it more likely to be a knackered valve stem seal.
Can you pin it down to a particular cylinder by looking at the state of the plugs? If they all look the same then it'll probably be an exhaust valve seal and taking the downpipes off should identify which cylinder.
Can you pin it down to a particular cylinder by looking at the state of the plugs? If they all look the same then it'll probably be an exhaust valve seal and taking the downpipes off should identify which cylinder.