I just purchased a 1991 Suzuki Katana GSX 750F and when I went to fill a pretty much empty tank, I could only fit in 4 gallons. The specs on the bike indicate that the tank should hold approximately 5.3gal and I am wondering: Where can the other 1.3 gallons go? The person who sold me the bike mentioned that there was a reserve tank, but I am not sure if/how to fill it up? Is it automatic? Any help here would be great.