What does that mean and how do I fix it? Thanks.

Usually when a 4 stroke starts burning oil it means the rings are gone allowing oil to blow by the piston, thus losing compression in the process. The back fire often is caused by the pilot jet being to lean, depending on when the backfire occurs. I think I'd address the top end problem first with new rings. Wouldn't hurt to look at your piston, cylinder walls, valves & springs while you're at it. If it's all original, some or all of the above could stand replacement as well.