| All you are doing is adding compressed air and listening for it to leak. A real leakdown tester has a calibrated orifice in the body and you are measuring the pressure drop across an orifice. The orifice should be sized for a specific pressure, usually 100 psi. That way, each psi lost is 1%. What you described will not give you percentage of air lost, it will only allow you to hear a leak. Sure, you the pressure on the gauge will change, but it is meaningless. It's not that "no one can figure out" the Harbor Freight tester, it's that they tried to copy the instructions from another brand, and the person who wrote the instructions didn't understand how the tool works (like you), and wasn't able to write accurate instructions. In it's current form, the tool will give you readings, but I am not sure of how legitimate they are. At least as legitimate as the "tool" you describe making. If you replace the right gauge with another of 0-100psi or more, the tool will function correctly. Alternatively, you can put a plug in the opening for the left gauge, and move the left gauge to the position occupied by the right gauge. With the quick disconnect uncoupled, you can pressurize the tool and adjust the regulator so the gauge reads 100 psi. Now, if you connect the quick disconnect to the hose leading to the spark plug hole allowing air to flow, the gauge pressure will drop and show you actual percent leakdown.
Mike ------------------------------------------------------
 |
