Why has no one mentioned that the head is rotated 90 degrees? With it rotated the engine will not cool properly.
Most flow through mufflers have the exhaust travel around the center tube and exit into the center tube from oppisite the exhaust port. Plugging the front of the muffler will increase the back pressure if the priming door is closed, but it will also cut back on the power available. Some engines actually run best without the pressure line to the tank as a few actually create a vaccuum instead of pressure. On those the tank just vents to the air.