True the PDF file does not say other than 8.5 : 1 Compression Ratio.
http://manuals.harborfreight.com/manuals/69000-69999/69727.pdf
Next I saw on GardenWeb about the Predator 212 should like most small engines have 120 psi and seems a lemon someone got had 30 psi. See (Chiefe's Post) I hope the valves were set right as otherwise a new engine will have too much over lap. My Briggs engine had the seat an valve wear to the point of no clearance. I fixed that by grinding the bottom of the valve stem and used a feeler gauge. Newer engines have adjustments wheel or screw.
http://forums2.gardenweb.com/discussions/1631207/predator-engine
Further web search got Ask.com got "How do you convert compression ratio to PSI?"
And with the equation:
14.7psi atmospheric pressure * 8.5 ratio = 124.95 psi (sea level) (pressure at altitude would be less and below sea level like Death Valley more)
http://www.ask.com/science/convert-compression-ratio-psi-825aedc74e6b59d7
And still further I found about Valve Cross Over that means cam lifter spec info needed and it gets it more refined. Other small amount also noted here about the head and head gasket This on Hotrod.com and also Hotrodders.com:
http://www.hotrod.com/how-to/engine/ctrp-0505-calculating-engine-compression/
http://www.hotrodders.com/forum/compression-ratio-compared-compression-psi-55398.html
Just want to add that if you are not really doing racing for competition the one used for general trouble shooting like 30 psi as opposed to 120 psi roughly, that gets the job done.
Hey I learned something. But wearing of valve and seat just so you know had my Briggs 3 hp 80's era engine not only low compression, it also had another problem related to valve wear.
The intake stays open after BDC and the compression stroke starts. A little of this is normal called cross over. With my clearance between tappet and valve stem bottom at zilch this is how it went.
2/3 of the piston travel on compression stroke the intake valve is still open wasting valuable pressure. Easy Spin Start or not this is too much cross over.
Hey the engine still ran, but it also was spraying gas at the air filter for a moment while it still had the intake open too long a time. The venturi of the carburetor was still effective and sucked gas from the bowl as normal, just pressure, not vacuum, was the force and fuel spray opposite out the opposite way.
Too many paper air filters wetted. A fuel soaked air filter was cause to have me almost stranded as it chokes for air and never starts again until it dries out. If you have time before night fall well just wait.
Prior the engine had the original air filter and that type was of an oil bath air filter type which was not really affected by fuel spray the wrong way. It probably did the oil bath no good, and wasted a bit of fuel too.
I changed the carburetor to a gravity bowl feed system as it fit better on the frame, but oil bath air filter was no longer a choice.
MT