No orifice? Not sure how that would work.
Work fine as long you not looking a percentage of leakage as I use an adjustable pressure regulator. Most times I just looking either a leaky valve or head gasket.
As for the working pressure you don't need 100 psi for testing just makes reading of leakage easier. Otherwords 100 psi in before the orifice and 90 psi out or 50 psi in 45 psi out equals 10%
leakage either way.
I usually use less than 40-50 psi. Even at these levels the crankshaft needs to locked in place on good engines. I start at zero pressure and work up as major leaks will show up even low pressure.
Air coming the following places:
Muffler - leaky exhaust valve
Carburetor air horn - leaky intake valve
Breather hose - worn or damaged cylinder/rings
Head area - leaky head gasket or warped head
Example I have Briggs 130000 series in the shop with an intake valve that is leaky even after grinding. I actually think it is leaking around the valve seat itself. It shows up even at only 20 psi when listening at the intake manifold.
