Well it may sound funny but.. some time ago there was a topic here about the Popping from an exhaust of a boxer engine, it was said that it's quite normal. but recently i've been noticing that on the garage door there are like black dots and its in the direction of the muffler, i also noticed it on a cement floor also aligned with my muffler. could it be that when it pops it spits something out.. fuel maybe? could this be wrong timing??