Plumb the tester into a heater hose or just tap into the drain petcock port (1/4" NPT) and run the engine without pumping up any pressure. If pressure builds up before the engine reaches operating temp, you have a compression/combustion gas leak somewhere.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!