I have an old Eska 5 hp outboard motor that I can't seem to keep running. A while back, several years ago it seemed fine but now it runs for about 10 minutes then quits. Can you help me to try if I'm doing something wrong to keep it running. It has an auxilliary tank and an onboard tanks as well. Am I opening the air vents properly ?? Should I close off the on board tank air vent? Any advice would be helpful. Thanks.