Leak Down Test On My New 418 Need Help?

Brian's right; it's true, at 80psi with the pistons at the top, it is dangerous.
but your results will be about as accurate as possible.

I use a 3ft pipe over the 20" bar. I set the piston to TDC, or a hair early. Then introduce the air very slowly, hanging onto the bar for dear life, and adjust the crank as may be necessary. If the crank flips over it will usually loosen the crank bolt.
My tester is home built with;one regulator,one gauge,a restrictor, and a ball-valve on the end . I dead head the gauge and set the pressure, then connect to the cylinder with the ball-valve closed, then slowly open the ball-valve. If the crank moves,I close the valve and reposition then repeat.
To figure the LD in percent with one gauge, you have to do the math. No big deal, and most times I don't bother, cuz I'm not looking for absolutes.

That's true, at 80psi with the pistons at the top, it is dangerous. Thanks Brian for the reminder.