Evinrude/Johnson 9.5hp Compression #'s???

[CaptainHook]

Ok, I started a thread a little bit ago about my 1965 johnson 9.5 having a "cough" at low rpm. I had taken the previous owner's word that the compression was 120 on each cylinder.

I checked it and it is more like 75-80 psi. Now, I have a 1973 9.5 evinrude (basically the same motor, right??) This one runs as well and has about 80 psi.

Are these really low #'s or is this what this motor should have. I always thought as a general rule a "healthy" 2 stroke had to be over 100 psi.

 

[bktheking]

Re: Evinrude/Johnson 9.5hp Compression #'s???

Should run fine with 80 or so PSI, these weren't powerhouse motors to begin with.

 

[Rick.]

Re: Evinrude/Johnson 9.5hp Compression #'s???

http://www.sschapterpsa.com/ramblings/OMC_9.5.htm

This is a good read for you. Your comp. #'s are fine IMO. Rick.

 

[kenmyfam]

Re: Evinrude/Johnson 9.5hp Compression #'s???

Numbers are O.K. in my opinion if it is a rope start.

 

[Rick.]

Re: Evinrude/Johnson 9.5hp Compression #'s???

Did 9.5's have electric starters? I live in a small world it seems. Rick.

 

[CaptainHook]

Re: Evinrude/Johnson 9.5hp Compression #'s???

Well, then if compression is ok I am back to the drawing board as to why it is running funky.....

No, they did not come with an electric start option.

 

[Rick.]

Re: Evinrude/Johnson 9.5hp Compression #'s???

You'll have to describe funky for us. Rick.

 

[cajuncook1]

Re: Evinrude/Johnson 9.5hp Compression #'s???

Ok, I started a thread a little bit ago about my 1965 johnson 9.5 having a "cough" at low rpm. I had taken the previous owner's word that the compression was 120 on each cylinder.

I checked it and it is more like 75-80 psi. Now, I have a 1973 9.5 evinrude (basically the same motor, right??) This one runs as well and has about 80 psi.

Are these really low #'s or is this what this motor should have. I always thought as a general rule a "healthy" 2 stroke had to be over 100 psi.

Have you check that you have a good consistent spark on both cylinders?

If you are trying to adjust the slow idle needle then it may be a little too lean. Turn it counter clockwise by 1/8 inch while your low forward gear on the lake to make it a little richer.

FR mentioned to me a while back that 9.5hp motors from year 1964 to 66 idle rough because vibration dampeners were not put in until 1967 if memory servers me right. My point is that if you are adjusting the slow idle needle to compensate for the somewhat rough low idle then it may be adjusted a little too lean.

If that is not the case and you have good spark on both cylinders, then you may need a carb cleaning and check your slow idle needle it could be damaged.


Hope you get it sorted out my friend,

cajuncook1

 

[CaptainHook]

Re: Evinrude/Johnson 9.5hp Compression #'s???

Not compensating for a rough idle. I don't even know how to describe what this thing is doing.

Anyone know if I can post video here???

 

[Rick.]

Re: Evinrude/Johnson 9.5hp Compression #'s???

I don't think so. You can post on you tube and then give a link though. Something you might want to try is to put an electric fan beside your motor and have it blowing so you know your not getting fooled by it breathing in bad air. I have done it with my 9.5 with good results. Also turn off the lights and look for spark going to ground. Easier to see in the dark. Rick.

 

[bktheking]

Re: Evinrude/Johnson 9.5hp Compression #'s???

The 1965 models were known for rough idle, I think there was a carb update that cured it. Post a youtube vid and it will be checked out. F_R might know something about the particulars about this.