I have a 4 stroke push mower. It has a primer bulb and if I prime it several times it will fire up, then fail after 2-3 seconds. However, I can get it started that way and if I push the primer bulb repeatedly after it is started, it will stay running. I have cleaned the carb, the bowl. I have checked the fuel line and changed the gasoline. Any ideas before I sling it in the woods?