Our 5+ year old tiller with a 5.5hp briggs-straton engine isn't starting up. We've done the burkholder choke, checked the air filter, carburetor, spark plug, and replaced the gas. The sparkplug ignites, and when I pull the cord with the filter off, puffs of white smoke come up, and a few times a little flame popped out too. Anything I can do before I take it to the repair shop?