[D-rail]

Make sure the ignition is off, and hold the throttle wide open, pull at least 5 times, maybe more, depends on if the tester shows an increase in pressure reading or not. Keep pulling over until the gauge shows no more increase. Repeat on both cylinders, no need to have the plugs in for the test. Pull as hard as you want, like you are planning on starting the engine.

The leakdown test, using about 100-130 pounds of air pressure, shows how much pressure is getting past the rings, preferably as little as possible, usually 3% to 5% is no cause for alarm, and shows a solid ring to cylinder seal... BUT, that can be enhanced if someone has put oil down the cylinder, which will throw off the true sealing ability. This may or may not show up until the sled has been run, then re-tested. I externally lock the crank at TDC (top dead center) for a leakdown test, most wear occurs near the top of the cylinder, and you are not exposing any ports to do this test. It needs to be hooked up to an air supply to get a good reading, not something many do for purchasing a sled unless real picky about a certain engine. Again, both (or three or more), cylinders need to be within ~10% of the others.

Another test, which is infrequently done, is testing the crankcase seal from both pressure and vacuum, where you need to block the exhaust and intakes to determine if the side seals are good. A low pressure/vacuum test of up to around 10 pounds is all this test requires.