compression on 90 mariner

[rosser1]

trying to find out what is good, bad and ugly compression figures on 81 model, 90hp mariner. i have done my research and can up empty handed on all old post. thanks.

 

[CharlieB]

Re: compression on 90 mariner

120 to 135 new, your results may vary depending on the quality of the gauge used. A cheap gauge may all read 80, another 100, a good gauge 120. As long as all cyls are relatively close to the same or at most within 10% of each other and the motor starts, then compression is not usually an issue.

 

[rosser1]

Re: compression on 90 mariner

yes motor cranks, but was running rough, i had to adjust carb set screws in order for it to crank back up after dying on the water. just trouble shooting, not like it to die while idling. thanks for the help.

 

[CharlieB]

Re: compression on 90 mariner

If it has been quite a while since the carbs were last cleaned, it may be time again. As the idle fuel passages get dirty and flow is reduced you start having idle problems, Clean and replace all gaskets to restore proper fuel flow.

Remember, if the idle circuit is dirty, so is the main, and running with a restricted main will fry a piston. It's just a matter of time, do it now and save a lot of time by not having to rebuild a fried motor later.

 

[rosser1]

Re: compression on 90 mariner

finally had time to do a compression test just to see what kind of compression i had, it is on 120 every time on all 6 cyclinders. i am going to reclean carbs, and fuel system.