1967 9.5 compression question

[JustinC]

Ive recently purchased a '67 Johnson 9.5 to try to upgrade the power to my 14' Alumacraft as my '76 Johnson got it up on plane but didnt get any speed. So I picked this little 9.5 up for under $300 but the compression is down at 75psi in both cylinders. So after searching the forum here I read about trying a decarb. I just did it today and followed the instructions exactly as it was posted on here and the compression didnt come up at all. This 9.5 pushes the boat ever so slightly faster than my 6 horse but the difference was almost unnoticeable. So my question is, A: ideally for the age of the motor what should I expect the compression to be, and B: Other than the lack of power (I could be wrond, but I feel that way) it purrs like a kitten from idle through wot, so should I susect the culprit rings, and cylinders? and C: I can't seem to find a source for the breakdown manual, any siuggestions?

Thanks in advance!

 

[DJ]

Re: 1967 9.5 compression question

At 75 psi I would say you are dead on.

The 9.5 should be faster than your 6. I would starting experimenting with trim and motor height.

 

[Rick.]

Re: 1967 9.5 compression question

Your compression is just fine. 9.5's seem to be lower compression engines. You should notice a real difference between it and you 6 HP. Check to see that you have spark at both cylinders. They run very smooth on just one but lack power if one is not firing. The way you load you boat and the tilt of the engine matters as well. Experiment with both. Best of luck. Rick.

 

[JustinC]

Re: 1967 9.5 compression question

Wow really dead on at 75psi? I figured it should have been around at least 100psi. But of course thats just from what I know about larger outboards and car engines, so I'm glad to hear that. My plan was to start checking plugs and for spark tomorrow, so we'll see. As far as loading my boat and trim, nothing has changed at all as far as loading goes since I've switched to this motor from my 6hp, and as far as trim, Ive played around with every trim angle and found the best, but still seams like it's lacking power. Because it does plane the boat out but just seems like it doesnt have that extra oomph I was expecting with the extra 3.5 hp. Thanks for the suggestions! Ill check spark tomorrow

 

[Rick.]

Re: 1967 9.5 compression question

One more thought. You could have a spun prop I suppose. Rick.

 

[jbjennings]

Re: 1967 9.5 compression question

I got about 80psi on the last 9.5 I worked on and it ran perfect. However, I find the 9.5's to be kinda wimpy on power compared to the early 60's 10hp motors. They feel like about a 7.5hp motor to me. ##just my opinion. If it planes you out, I think it's just running like a typical 9.5hp does. My '50s or early 60's models in 10hp would run off and hide from a 9.5hp.
Anyway, I too agree that the 75psi is not the problem.
Good luck,
JBJ

 

[JustinC]

Re: 1967 9.5 compression question

I thought of that, so I took the original 3 blade prop off of it and threw on my 2 blade from my 6hp that I bought a few years back and there was zero change in speed. Now that you guys are telling me compression is good, the wheels are starting to really turn and I'm thinking about spark. Regardless at this point, whether or not there is a real issue with the motor, I plan on selling it and going up to a 15hp. But at the same time I wanna make sure it runs like should whether or not I sell it tomorrow. Thanks for all the input guys, I'll keep you posted on what I find tomorrow.

 

[Rick.]

Re: 1967 9.5 compression question

Interesting to hear jbj's observations regarding the older 10Hp. models. I can tell you my 79 - 9.9 is much faster than my 73 - 9.5. I also notice the 9.5 uses quite a bit more fuel than my 9.9. I have a 15hp and it ran my 14 foot aluminum very well (I'm not overly concerned with speed but do want a motor that planes the boat well). The 9.5 has a unique look to it and it is a great slow trolling motor but I've heard parts are becoming less and less available. You could probably even put a 20 HP on yours. Check the rating plate. Rick.

 

[JustinC]

Re: 1967 9.5 compression question

Checked for good spark today, had it on both plugs. But decided to replace them anyway. I also noticed how much more fuel it drinks compared to my six, and was quite surprised at how much it burns. Hopefully later this week ill be able to get out on the water and see if maybe by chance a plug was not sparking properly at operating temp. But I think i'll be putting it up for sale soon as I said before, I'll just have to upgrade to a 15hp. Unfortunately the rating plate on the boat is no longer there so I really dont know what the max HP rating is. But I'm going to have the transom beffed up anyway here in the next few weeks so I'm pretty confident a 15hp will be just fine. Thanks for all the input and advice.