I am assuming that what you did with your reversed wires is send the ignition spark from the powerpack under the flywheel to the wrong secondary coil/spark plug lead. If this is the case, when the powerpack thought it was sending its ignition spark to the top cylinder, precisely when it was at top dead center, it was actually being sent to the bottom cylinder, which was a bottom dead center at the same time. This happened the same for the spark sent to the other cylinder. Both sparks were there, but their timing was not right.
So everything was working fine. Fuel went to the carb, into the crankcase, pushed into the combustion chamber, compressed perfectly and then no spark when the piston was at top dead center. As the pistion moved down the cylinder, that fuel lost its compression and was mostly sent out the exhaust, and then right when the piston hit its lowest point, your spark fired...but as I said, at the worst possible time. A motor will not run that way. Maybe a backfire if the exhaust was hot but probably nothing, like you were getting.
