Leak Down Procedure (Pic Heavy)

I've done them hot and cold on fresh engines with little measurable difference.But we are talking numbers in the zero to 3-4 percent!

On a used engine, there is a possibility for the pistons to be slightly cocked in the bore,due to the earlier mentioned cam-ground design,(post #13) which would tip the rings ever so slightly, and allow them to leak.Further more,with the cold used pistons, the worn ring faces may not be flat in the worn grooves, or centered on the piston, or there could be carbon involved or huge ring gaps.

However the amount of leakage is a concern. Here's a quote from Smokey Yunick talking about leakage over 8%.
" This doesn't sound like very much to worry about,but you have to remember that only 1/3 of the heat energy(pressure) developed by each cylinder is actually going to push the piston down. So, if 8% of the cylinder pressure is leaking away, you are theoretically losing 24% of the recoverable flywheel horsepower."
He goes on to say that around 5-8%, should be considered rebuild time.
If your tool is truthful...........There is a problem!
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2-cycle outboard engines are a whole different animal. These engines are cooled by sea/lake water. They go from idle to full load-WOT, and back. They spend huge amounts of time at full-load WOT. To cope with this abuse the pistons are laughably loose in the bores. When cold, there is no way to keep the pistons from rocking, and thus no way to keep the rings in full contact with the cylinder walls. I'm not surprised to see 20% leakage on an outboard. They also have huge head chambers and low compression, due to the 2-cycle design.They make power because they fire twice as often as a 4-stroker, and usually operate in a very narrow rpm band, allowing the designer to optimize the port layout.