Yard vacuum will start and continue to run for less than 5 minutes with no problems, but then starts to conk out like it is running out of gas. The gas tank is full, oil levels are fine, new spark plug just put in. The bag is sitting securely on the kill switch where the bag attaches to the vacuum on the back. When the vacuum starts conking out, if you lift and tip forward it will begin to run again good, but as soon as you put it back down to the ground it conks out. Difficult to start after this happens as well.