Evinrude 7.5 idle

[fleetwin]

It is fine to check the compression cold, but beware of variances in compression readings between various gages. These engines have relatively small combustion chambers, so these minor variances wouldn’t account for much in engines with larger combustion chambers, but may affect normal readings on this engine.. In any event, these engines have relatively low compression, so you will probably see readings between 70-80PSI, which is normal for these engines. The compression readings should be the same for both cylinders though.
Is this engine “new to you”? Or, have you owned it and used it for awhile. If you have owned it, when did it last idle properly?

[outbdnut2]

To add to what Fleetwin said in the post above, if your compression gauge has a hose, and if the gauge relief valve is at the gauge end of the hose, the volume of the hose will add to the volume of the cylinder and give a low reading on small cylinder motors. I have one of those gauges that reads 40 pounds compression on a JW 3 HP Johnson, and if I remove the hose and hold the gauge with out hose but with a pointed rubber end in the spark plug hole, compression reading nearly doubles. The bigger the cylinder, the less the error becomes.
Dave

[bob-d]

A tip to ground the spark plugs when doing your compression check it to use small magnets (Home Depot etc) to hold the plugs in place on the block.
Bob D

[seakaye12]

It’s a long shot but check the slow-speed needle to verify that it is the correct one. Sometimes they get damaged or lost and someone replaces it with one that is not exactly the same. Try to compare with another engine if you have access to one.

[Mumbles]

The original author of this thread hasn’t been here since last January so I suspect he either found the problem or gave up.

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