I recently purchased a two year old 10 hp Troy Built wood chipper. I've used it for about 4-5 hours and recently had to add a little oil. I added the correct type as per the manufacturers instructions. It started up just fine and after 15 minutes or so I shut it off to empty the bag. Once the engine was off it was clear the bag wasn't full, but when I try to pull the starter cord it is stuck. I let it cool down, but nothing changed. I also removed and blew the dust out of the air cleaner since the leaves etc were very dusty. This also didn't work. Any ideas?