i'm guessing that you caught them before they got their tanks re-filled. There is a bunch of sludge and gunk that collects in the bottom of the tanks, not to mention moisture. if you continue to have problems you may want to consider either adding the external fuel filter mod. Personally, i try to find stations that are pretty busy, as they tend to get fuel delivered more often. Small, out of the way stations may have old fuel that has had time to mix with the gunk, and/or may be low, as it is not always cost adventitious for them to fill up the tanks as often.i work on chainsaws and lawnmowers for a living and we see a lot of problems caused by fuel .