The proper way for the most valuable results is:

1) Run the engine until warm to hot, but not to operating temp necessarily.
2) Remove ALL the spark plugs,
3) Block the Throttle wide open (or at least open).
4) With k-jet, block the air plate open if possible, or just slip the intake boot off the throttle body bypassing the air meter.
5) I use a "remote starter switch", in this way the ignition is left OFF, so no spark and no fuel worries. You connect one end of a switch to the "S" terminal on the starter, and the other to +12v, when you activate the switch, the starter engages, but it's ONLY the starter.

You should get readings between 90-120 psi. It is more important that they are close than what they actually are.

Oops! Only crank about 5 tiems per cylinder, and it is VERY helpful to have a battery charger on while doing this. Cranking speed WILL affect your results.
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JohnG 1989 245 MT @216,500