My 97 Nissan D21 is getting fuel into throttle body when I start it up. Been using all morning to haul off yard trash. Backed up to a heavy object to load, Got in to leave and when I turned the key, all I got was dim dash lights and a clunk (like a dead battery). Opened hood to found problem and saw fuel had come out of air filter. Opened air filter and saw fuel draining back down throttle body. Like to know what the problem could be.