FWIW, I'll give you an example that goes to what Slomo suggested. I had a customer with a Craftsman tractor with the gas tank just under the front shroud. The space between the fuel cap and the dashboard was relatively tight and as a result collected grass clippings and more importantly dead leaves. My customer wasn't too careful about clearing around the cap when he filled up. He got a number of big chunks of dead leaves in the tank. They'd slosh around the tank and eventually they'd cover the output of the tank and it would choke out. Time varied, and degree of choke out varied. Good repeat customer though even after I told him how to prevent it, LOL! Definitely do Bert's test as well!
Good luck!
Good luck!