I just picked up a Vulcan 1500. It is mechanically sound (a mechanic went through it before he sold it). The only issue I have found is the tank will only take 2 gallons. All the spec sheets say it should hold 4. The feul gauge reads the two gallons (I filled it on E and it reads Full now). Any suggestions? Is there a cross over that could be clogged? Am I missing something simple?