I have come across the opportunity to obtain a '91 Mazda 626. The car runs and drives, but the current owner says it has low compression in 2 cylinders. He also said his mechanic claimed it has something to do with the valves in these two cylinders. I'm guessing this is either caused by a burnt valve or possibly just bad carbon deposits not letting the combustion chamber seal. I guess my question is this- if the problem is maintenance-related and not a detrimental mechanical problem, what would be the best and most effective way to go about making this engine run better? I.E. making the valves seat better and restoring lost compression. Any info would be greatly appreciated as I am planning to fix this car up and give it to someone I know who is in need of one.