Small Engines (Lawn Mowers, etc.): husqvarna engine problems......, automatic compression release, blown head gasket

Question
i have an older husqvarna z turn mower with a kawasaki FH721V engine on it...the problem im having is the automatic compression release seems to be not working properly....the engine starts  fine but after a few minutes the engine develops a hissing sound like an air line leak on an air compressor....it was real bad up until today...i took both heads off the engine thinking i had a burnt valve or piston damage...nope both cylinders were fine..i tore the heads down cleaned them up...and cleaned the valves after doing this i re assembled the engine...and it started right up and ran 100 percent better...that mower has never been easy to start...something is still not right though..it still has the " air leak"   issue only much much quieter...is it the valve lash thats not right?...or possibly the govenor arm?...ive gotten a crash course in mower repair this past 2 weeks i'm trying to keep up with 8 landscape crews that seem to destroy our equipment on a daily basis....please help me fix this problem with our mowers....how exactly do you adjust the compression release?...what am i doing wrong?..

Answer
Well, an ACR is just that, automatic. There is no adjustment, it is just a lever on the cam that opens the exhaust valve on startup to help the engine start easier. When running, the ACR flips out of the way and does nothing. What you have sounds like a blown head gasket, warped head, or a simple exhaust leak. The only way I know to diagnose this is with a leakdown tester.