I have a rebuilt engine...currently = with 6,000 miles. Compression shows 120 on all with the exception of number one it = has 90psi. Are air cool engines notorious to burn valves? I did a leak down = and air is coming up through the intake manifold. I even backed off the valve = lash adjusting screw to ensure that the valves were seated and of course = the piston at TDC. Another observation was when I = adjusted the valves (some valves) would move side to side while = turning the adjusting screw like if there was to much play between the valve guide = and valve stem!!!! is this normal for air cool engines? I replaced the = adjusting scews because the rebuilt shop kept the old ones on and they were = flat or mushroomed. They are suppose to be tapered to a point somewhat. I = noticed that the engine started missing and a metalic sound just like a loose = valve along with an exhaust leak. Can anyone tell me what has happened here.