Compression test - how to questions

1973 Evinrude 135383M

So, JB created a great basic article, but the problems for most boat engine buyers is more complex.
Lots of articles refer to gang plugs - forget about it, they do not exist. I did Google for weeks.
Let's assume that you will use the battery power from your tow rig ?

Remove all the spark plugs and connect the wires to 1) outerspace, 2) grounded to the engine lift,
which is also grounded to the tow vehicle jumped to the tow vehicle.

Disable the the manual choke clamp at the engine and override to open.

Insert compression tool into each cylinder and read results, while jumping the positive cable to a jump to the red connection at the bottom of the solenoid.

I have purchased and read the owner's manual and SM

It is very complex for most of us to do a compression test on a new purchase. What can we do ?

Thanks
Ed

Re: Compression test - how to questions

DO NOT use the start function of your key. Make a jumper from + cable to solenoid input to intermittently engage starter. That disables ignition.

Throttle and choke position are not important.

Re: Compression test - how to questions

A field compression test may be misleading. If you pull out the plugs and turn the flywheel by hand, it should move easily and silkily. you should be able to feel a slight crankcase compression as the pistons move down (two Cycle engines.) If you put your thumb over the plug hole, as the piston comes up, it should force your finger off the hole.: The engine will either have compression or if it does not force your finger off, it has no compression--don't buy it unless you discount for a complete rebuild.

These tests only require a plug wrench, are simple, and give a general idea of engine condition.