I've got a 2007 21" walk behind that I haven't used in about two months. I drained out the old gas and put a little bit of new fuel in the tank but it still isn't working. The engine starts, runs erratically for a few seconds, then dies. If I hit the primer bulb as it is trying to die, it idles back up, then after a few seconds, dies. If I hold the primer bulb in, it stay running at a normal RPM. The engine is a Briggs & Stratton 650 Series 6.5HP for those who may have this mower and can help me. Any help is appreciated. I gotta try to get this mower going by tomorrow morning! Yikes.