Having problems keeping flame burning in furnace.Oil furace hadn't been used in 2 years and had oil delivered recently.We figured the tank would be close to empty but were told after it was filled that it was already over 1/3 full. Furnace would light up with yellow flame but then turn blue and then safety kicked in. The furnace is making loud rumbling noises off and on but can't keep furnace going long enough to figure out anything.We've replaced nozzle,transformer,oil filter, cad cell and tested pump pressure so now we're wondering if the oil was bad from sitting in the tank for 2 years. Oil seemed a little on the thin side as well.Any Suggestions?