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How to Check Compression, 2-Stroke Outboard

Updated: Nov 24, 2023

To check the compression on a 2-stroke outboard, you can try these steps:

  • Remove all spark plugs, clean, and dry the spark plug

  • Screw in the compression tester finger tight, one cylinder at a time

  • Ignition off, open the throttle to 100%

  • Crank the engine about 4x, until the gauge stops increasing

  • Record the reading

  • Repeat for each cylinder

Here are some tips for checking compression on an outboard engine:

  • Warm the engine before doing the test

  • Count the pulses when cranking

  • Use the same amount of pulses for each cylinder

A good compression reading for a 2-stroke engine is between 110 and 130 psi, as the color change from red to green indicates on the Buckshot Racing #77 Compression Gauge.

The difference between the highest and lowest readings should be no more than 10%. Low compression can be caused by a leaking piston, piston ring, camshaft, head gasket, or valves. To test for this, you can add some oil to the cylinder.

If compression is low, it's recommended not to run the engine. Pull the cylinder for further inspection. It could be time for a build before more damage is done by running the motor.

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