The leak down test does not use oil. Oil can be used during the compression test to see if it helps the rings seal better. Tablespoon is fine in large car cylinders but it too much for these small motorcycle engines and can indeed give false high readings as the oil takes up space in the cylinder effectivly raising the compression ratio. All you want to do is put enough oil in so it coats the cylinders and rings trying to make them seal better. Leaking valves or head gasket will not get better with oil. The leakdown test is done with a tool that puts compressed air in the cylinder with it at top dead center compression stroke. Then you listen to where the air is escaping. The leakdown tool has a calibrated gauge that tells you the amount of leakdown in the cylinder. But it is easy enough to rig up a setup that threads into the cylinder and connects to an air supply. I just use an old compression test hose and connect to my air compressor with a regulator so you can slowly up the air pressure and see where it is leaking. Too much air and you will make the engine spin over, normally if you have a leak it is pretty obvious. Out the exhaust...leaking exhaust valve, out the intake...leaking intake valve, in the crankcase.....past the rings, out another cylinder.....blown head gasket between those cylinders. The amount of leaking to me is irrelevant, if it is leaking I am going to tear down and fix it so I dont need a tool that tells me percentage of leak....because I dont care. A small amount of leak is always going to happen because rings can never seal 100%
