When I start it I hear it prime, after 5-10 seconds the burner ignites, it'll run about 10 seconds then cuts off with a small puff of smoke. I've changed the oil filter, checked for leaks (though I have no way to check the vacuum on it) and even tried a cad cell I had in a previous burner. I'm still thinking it might be the cads, but the puff of smoke thing is bothering me. Any ideas before I get ripped off by some heating guy?