Small Engines (Lawn Mowers, etc.): Briggs Stratton 5 hp, wire armature, briggs stratton

Question
Marc, In you return message you mentioned the centrifugal decompressor, I remember seeing this when I had it apart. Don't know what to do with it to increase the compression. You didn't say in your last answer. Can you tell me more about it and how to improve compression? Didn't really look too close at it when I had the crankcase cover off, but it is plastic with metal weights. Don't think it was rusted, it seemed to move freely. And what about the governor, the arm has a spring which is attached to a lever which has the throttle cable and wire armature to the carburator. the governor lever seems to be in the up position with motor not running and only moves about a 1/4 inch when pushed on. Any help is greatly appreciated. thanks, rick-----------------------
Followup To
Question -
Hey Marc,
I recently dismantled a tiller B&S 5 hp which had sit up for 2 years. The camshaft, driveshaft, piston rod and rings, intake/exhaust valves were all rusted and frozen. replaced after grinding the rust off with a plastic wheel grinder on a drill and used wd40 to loosen parts. Everything back together with new gaskets in clyinder head and crankcase and new piston rings. Intake/exhaust valves were frozen wiht rust and required about an hour of careful prying/pushing and wd40 to loosen. same with the connecting piston rod and pin in piston head. Engine cranked on first pull, but smoked alittle. ran for about half hour hoping the smoke would clear. Heard loud squealing sound and engine stopped. Pulled easy enough, but wouldn't crank even with gas/ehter spray in sparkplug hole. Dismantled and everything seemed alright internally. Checked compression and measures 60 psi. (Think it is suppose to be 120 psi). Good suction sounds when turning the flywheel/crankshaft. Sparkplug is firing (removed from hole and pulled start cord). Only thing I can think of is the intake/exhaust not closing completely. both seem not to be completely flush with the clyinder head valve holes. Either seem damaged or bent. Any ideas where decompression coming from?
thanks,
rick
Answer -
If you have the engine apart, you may notice the camshaft has a centrifugal decompressor on the exhaust lobe.  This serves to bleed off compression through the exhaust at low RPM (such as when starting) and has weights that "fly out" centrifugally when RPM increases to restore the compression level.  If you heard a look screech, it's likely the starter clutch is at fault (especially if this engine has been sitting) and will need to be replaced.  If you have an issue with the valves, you may need to do a thorough valve job (which may include replacing the guides too)  Hope this helps.  

Answer
You cannot change the compression with the decompressor.  The decompressor reduces compression to make the engine easier to turn over while starting.  Then whatever compression the engine is capable of is what the engine runs at.  The centrifugal weights also run the governor arm.  The distance (1/4") you mention is about right for the governor arm's movement.  Not sure what answer you are after but you cannot check the compression like you can on an engine with no decompressor.  The only way to make sure you have proper compression is to ensure the valves are sealing and there isn't a large ridge on the top of the cylinder (from wear).  Even if the engine has high hours and the cylinder is worn, it will usually run but will consume more oil.  Valves are the main reason for a low enough compression to prevent starting.  Hope this helps.