Try pumping some of that gas you're getting from the tank into a bottle, pour a little out on the ground, and toss a match into it. I'll bet it's hard to light, or it won't burn at all. I've seen situations where gas went stale enough in a very short time that the engine simply wouldn't run on it. It's also possible a little condensation formed in the tank, and you're actually pumping water, not gasoline.
Jerry
