1988 Johnson 225 Looper Compression Test

[RPruitt]

What is the correct procedure and PSI for a compression test on this engine ? If I remove all the spark plugs, the bendix on the starter disengages because the engine is turning too fast. If I remove the plugs one at a time and run the starter I get 75 - 85 PSI on all cylinders. I have checked the compression periodically over the last 9 years and consistently get these readings using the one at a time method. The engine runs great with top RPM around 5500 (15 x 17 prop) on a 23 ft Proline 230. I also use decarbonizer every 50 hours or less. Do these compression reading sound OK?

 

[Dhadley]

Re: 1988 Johnson 225 Looper Compression Test

Sounds like a typical looper to me. The only thing I might suggest is to raise the motor to get a few more RPM's on top. That will relieve the stress on the motor throughout the entire RPM range, improve your holeshot, increase top end slightly and help with fuel mileage.<br /><br />Good luck!

 

[RPruitt]

Re: 1988 Johnson 225 Looper Compression Test

Compression Test procedure ? Is engine supposed to be cold or hot? What is proper PSI ? Should all spark plugs be removed, or one at a time ? I assume test is to be performed with starter motor, not engine running with one plug removed at a time ??

 

[Dhadley]

Re: 1988 Johnson 225 Looper Compression Test

It can be done either cold or hot. Some prefer one or the other. On the loopers you will find that most of the the time you will need to remove only one plug at a time to keep the starter engaged. And PLEASE don't try to do it while the motor is running!<br /><br />Good luck!

 

[forgetaboutit]

Re: 1988 Johnson 225 Looper Compression Test

Dhadley,<br />When you refer to raising the motor what are you talking about?<br /><br />Thanks, KEN

 

[Dhadley]

Re: 1988 Johnson 225 Looper Compression Test

Raising the motor verticaly increases the X dimension. Basically you remount the motor so the propshaft is closer to the surface of the water. This is done in small increments to find the "sweet spot" for the type of propeller you are using. <br /><br />Raising the motor, or increasing the X dimension, gets more of the gearcase out of the water which means less drag. Less drag improves the overall performance and usually the life of the motor. <br /><br />It's not unusual to raise a motor on a given boat and find you can actually turn a larger pitch prop at higher RPM's. I have seen boats pick up as much as 14 MPH. It depends a lot on the boat's hull design. <br /><br />Most of the time when the holeshot is not very good, the person will go to a smaller pitch prop which 97% of the time means a better holeshot but less top end. We always try to enhance performance by reducing hull drag and/or propeller slip percentages. <br /><br />The good thing about raising the outboard motor is that its basically free and can be undone easily. <br /><br />Hope this helps!