Leave the key off and put the throttle at WOT (not that it makes any difference) using the throttle only button or warm up lever, then use a jumper on the solenoid to crank the motor.
NOTE: LEAVE THE KEY OFF.
This is the best idea I have ever seen. Outstanding, Mr. Moderator!
For Richard's benefit, somewhere back there Merc came up with the 40,000 volt (unloaded) fast rise, capacitor discharge ignition system. It's been awhile since I retired and I forgot the number, but 40kVolts can jump a lot of things that you don't want jumped (arc tracking, voltage breakdown of lower rated components) if you don't have the plugs connected and grounded. Keeping the ignition off prevents the development of the voltage and jumpering the solenoid gets power to the starter.
The solenoid excites by energizing the small terminals where one is grounded to the block usually (battery -) and the other receives 12v from the ignition key in the START position. The exciting current is small so you could get a couple of alligator clips and a piece of 20 AWG or better insulated wire and make a jumper to get 12v from your input ⅜" stud (convenient place to grab it) on the solenoid over to the small terminal of the solenoid that's not grounded.
Obviously plugs are removed to allow spinning up the fastest. Fresh charge on your battery. All the manuals recommend opening the carbs (WOT) to let some air in to compress, fast idle as stated is an easy place to grab that. That way you can be in N so you don't have to worry about the prop turning. The manuals also recommend EVEN numbers, like within 10# some say, 15# others, as a must (as GA also suggested) with my last manual saying "if less than 120, expect problems". If you are flunking the test want to know if you have worn rings, squirt some 30 wt oil in the cylinders (all around) and run the test again. If your numbers jump 20# (for a number) you are pretty far down the curve. Course you need to have an accurate instrument used properly!
On what you squirt in your carbs for attempting to start the engine for whatever reason, not associated with this test, use Sea Foam Aerosol...Walmart and auto parts stores carry it...red label, white pint can, about $7. SF contains naptha, alcohol, and light mineral oil which your 2 stroker needs for internal lube that a lot of other products don't contain and it will start and squirts will keep it running when used for testing....like when you are troubleshooting a dead engine and want to know if you chase spark or gas.
