Hop in, turn the key, it starts, and idles fine. Run it for awhile, and it dies. Crank crank crank.........No start. Get out, open hatch, unscrew fuel/water separator, tighten back up, starts and runs. Goes for awhile then dies again. Thought it was a plugged vent hole in the gas cap, so cleaned, and it ran better for awhile. Thought I had problem solved, but it just did it again. Ran with gas cap off, same thing. Any ideas?