I forgot to mention, if your arch does not have airtight doors, you should be able to get the flame to shoot out of all the cracks around the doors. Turn the blower speed up until you see this happen, then slowly slow it down until no more smoke/flame is coming out the doors. This is the correct speed to run at. It will be slightly different everyday.
If you have the blower at full speed and you don't get smoke/flame out the door cracks, the blower is too small. Get a bigger one and try again.