I also had a similiar problem with oil burning at a rapid speed. It turns out that I am losing compression, which in turn means that I am losing power. Check your spark plugs to see if there is any oil on them or on top of your pistons. If there is, then your piston rings are bad.
This is not entirely correct. Your spark plugs could be covered with oil because of a few reasons:
1) Valve stem seals are bad leaking oil into cylinders
2) Valve guides are overly worn and need replacing
3) PCV valve is not working correctly and there is excessive oil going into the intake manifold and through the intake valves into the cylinders
4) piston rings have no compression left.
To tell where the oil is coming from, do a compression test. If the cylinders are holding a good amount of pressure (150-210psi) then there is no way the rings will cause excessive oil to get into the cylinders and burn out the exhaust. If the piston rings are bad, the compression test will show a low reading and/or you will be getting a lot of blow-by when you take the oil filler cap off and put your hand over it while the engine is running. Also will see smoke coming out the oil fill tube with the blow-by.
Another good test besides the compression test is a leak-down test. You can pick these up at Harbor Freight for $40.
Here's a video on a leak down test
http://youtu.be/ofSiTGeLXvc
My motor was burning a ton of oil in the morning and going through a quart a week and the plugs looked fine!
Really bad oil leak in cyl 1
A lot of deposit on the piston head
Valves looked burned as well
After deposits cleaned
New Head ordered
