I have a new Hustler Z. There is a little valve with a red plastic handle mounted between the seat and the right hand fuel tank. Both rubber fuel lines run to it. Presently the handle is pointing toward the front of the mower and the mower seems to be operating off of the the right fuel tank. I moved the handle 180 degrees to see if it would operate on the other tank and it seemed to run out of gas and die. I moved it back to it's original position and it started and ran OK. Is this the tank swap valve and did I do something wrong? Could I have a bad valve?