whats a good compression number

[pedixon]

Hi all

Getting ready to decarb my 1989 15hp evinrude, am going to buy a compression tester and check em , just wondering what should I expect for numbers. Never been decarbed before. Also a question about gas. Is there any benefit to running 89 octane vs 87.

PS - Welcome back bktheking

Thanks Phil

 

[tashasdaddy]

Re: whats a good compression number

no benefit for anything other than 87 octane, other than wasting $$$. rppe start motors, 60 -70 psi after 3 pulls. test before then after. also new fuel lines. ethanol. see the top secret file.

 

[Whoopbass]

Re: whats a good compression number

A good compression reading will be around 90 psi. They will still run fine when the compression is 60lb+ psi.
A rope start motor will give you a lower reading then electric start since you can't get the motor spinning as fast. I think my 25 has a 15lb difference between rope and electric but used 25hp motors usually have around 100-120 psi and the are harder to pull so you probably wouldn't see the 15psi difference with your 15hp motor.

 

[pedixon]

Re: whats a good compression number

thanks for replys


Phil

 

[kenmyfam]

Re: whats a good compression number

Readings should generally be within 10% of each other for each cylinder.