Explain leak down test.
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A leak down test is used to diagnose problems with your engine. There is more things that can happen in 4 strokes that I would normally test for like leaking valves. This is just a basic description of how it works. I would go by the recommendation instructions on your tester.
"Basically" the testers look like an engine compression tester that also uses compressed air to build the cylinder pressure compared to pulling the engine over to build compression.
The piston must be at top dead center and fill the cylinder with the compressed air using the spark plug adaptor that should be included. Note that some older testers only had standard plug threads and many sleds and many newer cars have metric threads. Mine has the metric and standard adaptors.
The test results are compared to the other cylinders.
The leak down can test things like a leaking head gasket that you might find bubbles in the cooling tank while testing.
Each motor will have its own specifications from the manufactures. No engine is completely sealed. Each motor will have leakage depending on miles, type of oil used ect.
I like to make sure Im comparing apples to apples, so if you do different test, make sure the motor is the same temperature between tests and record your results.
To locate a leak listen for escaping air from things like intake manifold, muffler if exhaust valve leaking (4 stroke), dipstick or oil fill port if the piston rings are leaking again 4 stroke , etc.
I will post up some pictures of doing it on my sled when my buddy finds my tester and a few other tools he borrowed.