70hp johnson compression

[DOC30]

I have just bought a 1978 70hp. Johnson Outboard and was trying to get info. on the compression.. What is the specifications for a compression test.. I check all three cylinders and they were from 90 to 120lbs.. Is this good compression for this motor?<br />The motor seems to run fine, but hasn't got alot of throttle.. After changeing the plugs I noticed that the top two are firing pretty good, they look like there fine.. The bottom one is clean as new.. I checked the firing and It's firing fine..I guess the carb maybe the problem.. What do you think?? I appreciate any help.. *** bless... DOC30

 

[JB]

Re: 70hp johnson compression

Howdy, Doc. Your compression is NOT-OK. Not only is 100# the minimum acceptable, 15# difference between high and low is minimum acceptable difference.<br /><br />Until that is fixed, other issues are academic.<br /><br />Good luck.<br />Red sky at night. . . .<br />JB

 

[DOC30]

Re: 70hp johnson compression

Hey, glad to get a reply... Thanks J.B.//<br />I decided to check the compression again after your reply.. I thought there for a minute I was going to try my first rebuild on a boat motor.. I wasn't real thorough with the first test I did.. On the second time around I had 120 lbs. on all three cylinders..There was no varance at all.. That was a big releive.. I decided to go ahead and check the carbs., and found no gas in that bottom carb. bowl.. I went ahead and took off the carb. and cleaned it out good, it was alittle gummy in the bottom..The needle and seat didn't look to bad but I decided to call a marina thats down the road and they had needle and seats sets.. I went ahead and replace all three carb. needle and seats. plus a good cleaning..Went ahead and replaced all the gas lines including the bulb. Put it all back together and went to try it out this afternoon.... She ran like a champ.. The only question I have left is my prop has some bad places in it, and I was wondering what do you recommend? Should I go back with the original or try something else..I really do appreciate your help... Thanks And *** Bless....DOC30

 

[JB]

Re: 70hp johnson compression

Get your prop rehabbed at a local shop. Buy a cheap spare prop to keep on the boat. Congratulations on getting her going. That OMC triple has been one of my favorites since they were introduced.<br /><br />Red Sky at night. . . . . <br />JB