How much compression should a Mercury outboard have?
Results vary depending on whether the outboard is a Four-Stroke or a Two-Stroke. Good results for Four-Strokes should be 180-210 PSI, and Two-Strokes should be around 110-130 PSI. Here is everything that you need to know about outboard compression tests.
What should the cylinder compression be on a Mercury outboard?
From my research, cylinder compression values that people say are “acceptable” for low horsepower outboards seem to vary. They not only vary from the reporting individual but from manufacturer to manufacturer. For instance, a fully functional Mercury 25 Hp cylinder compression value may be significantly different than that of a Johnson 25 Hp.
What should the PSI be on an outboard compression test?
Results vary depending on whether the outboard is a Four-Stroke or a Two-Stroke. Good results for Four-Strokes should be 180-210 PSI, and Two-Strokes should be around 110-130 PSI. Here is everything that you need to know about outboard compression tests. How to do them and what the results mean for you! What Is A Compression Test?
What should the cylinder pressure be on an outboard?
Since most of us do not live at sea level, the actual ideal theoretical cylinder pressure should be slightly less than that since the atmospheric press is less at higher elevations. Good working outboards generally have a compression of 75 to 85 psi.
What should the compression be on an Evinrude crank?
However if you watch the end my video below you will see that my 1979 Evinrude 6 Hp cranks easily cold ( 2 pulls) with 60 psi compression This source says the older two stroke outboards below 25 Hp should be between 75 and 85 psi. This source seems to confirm with my understanding that 60 psi in older outboards can sometimes be OK.
From my research, cylinder compression values that people say are “acceptable” for low horsepower outboards seem to vary. They not only vary from the reporting individual but from manufacturer to manufacturer. For instance, a fully functional Mercury 25 Hp cylinder compression value may be significantly different than that of a Johnson 25 Hp.
What are the compression numbers for an outboard engine?
Also the numbers will be different bank to bank. The standard for compression these days is and has been that overall, the cylinders should read within 10% of eachother whatever the reading is. That takes the differences in model years, engine models, brands, and compression gauges out of the game.
What causes a bad compression test on a Mercury 2 stroke?
Even a small leak will result in a poorly performing powerhead as the fuel mixture will become lean causing the temperatures of the cylinder to increase. Lean air and fuel conditions increase cylinder temperatures beyond factory specifications.
What should the PSI be on a 2 stroke outboard?
What I have found unanimously is that the relative compression values between the cylinders should be within 10%. This source says modern two-stroke outboards should be in the 90 to 105 psi range.