Just something to note with compression testers, when using compression testers like the RYCO one in the image below the black hose and the fitting that screws into the plug hole adds to the combustion chamber volume in the head ,this gives you a false compression reading.The compression reading is 20 PSI lower than what you will read on a short compression tester like the one below with the green scale.
Both compression testers were used on the same mower the Ryco reads 50 psi and the short comp. tester reads 70 psi.
I use 50psi as a minimum reading when using the RYCO gauge.
