Compression numbers on a 1986 Yamaha 70hp 2 stroke

[HalibutZach]

Hi Everybody, I am a newbie here as of today, I did a search on my topic and could not really get a definitive answer. What should the compression numbers be on a 1986 Yamaha 70hp 2 stroke motor. What are good numbers and what is the lowest acceptable number?

 

[robert graham]

Something generally in the 100 to 140 PSI range, but what's most important is that all cylinders readings should be within about 10% of each other....for instance, 2 cylinders at 120 PSI and 1 cylinder at 80 PSI could indicated a problem on the low cylinder....like stuck piston rings or scored cylinder walls, or other issues...

 

[HalibutZach]

Thank You Robert...................

 

[tommarvin]

I would use 100% synthetic two stroke oil, Marine gear lube, Fogging oil, etc that's the best you can do if the motor breaks just fix it, You do a compression test with all the spark plugs out, test each hole with some amount of cranking time cant remember how long.