Last season I only put 100 hours on our institution's new Exmark HP ZTR. I figured the fuel filter would be good to go for another season. During my third cutting this spring (6 hours total)and just filling up the tanks, the fuel filter clogged up to the point the mower engine started running rough, sometimes shutting down. I pulled the filter and sort of backflushed it in can of gas. A bunch of "goo" came out. Put it back on and it runs fine. Do you think this was a fluke....maybe a glob of something out of our storage tank (has it's own filter)? Or, should these dinky filters be changed annually regardless of hours? FYI, I stored the mower full of fuel, treated with stabil, and ran the engine 1/2 hour per month to keep things lubed, etc.. I think this is the first time ever that I actually had a fuel filter clog enough to affect an engine.