I have an extra motorcycle that rarely gets ridden. Had new tires and tubes put on last spring and havent had any problems until recently. The bike sat for about a month, and the front tire was completely flat, rear tire was fine. I filled the tire and checked for punctures/leaks and could not find any. I rode it around then parked it in the garage. Checked the tire the next day, no pressure loss. I let it sit in the garage for a week without moving it, rechecked the pressure, still no loss. Now 2 days later, it still has not moved and the tire is completely flat again. This makes no sense to me, any suggestions?