Trouble free until last year. I am the original owner. Presently starts easily but occasionly will cut out. Usually this occurs when it has been out for an hour or so. On restarting it will then not idle well; example when docking. To date: a tune up (pts and plugs), another fuel filter even though it is replaced each year as a matter of routine maintenance., removal of the anti-siphon valve at the gas tank have been to no avail. The vent is functional. Idle is set at 650 rpm. Use Sta-bil each fall but present petro is new this season. Any ideas?