Mercury Optimax 150hp Compression test

[390Express]

I would like to do a compression test of a Mercury Optimax 150, but no battery/keys. Can I use an electric impact (spins around 550rpm) ran in reverse (I believe it's a LH rotation engine) with a socket on the flywheel? 15/16 socket?

Bonus question, any tips or tricks to pulling the outboard off? Lift by the lift ring, any tricks or tips to disconnecting the steering/gas line/wire harness, or is it all pretty straight forward? Only outboard I've ever removed is a 40hp yamaha, and I just threw it over my shoulder.

 

[faztbullet]

Pull plugs and jumpthe starter with cables

 

[Edchris177]

I wouldn’t use an impact driver. Those are made to impart a bunch of very short hammer blows/second. You need constant torque.
Do as Fbullet says.