1990 Johnson 120 has issues

QUIC

Cadet
Joined
Jul 30, 2010
Messages
14
I bought this motor about three years ago to replace another nonrunning motor. Previous owner stated it ran well until it wouldnt start one morning.the motor was super clean and it was 20 hp more than my old motor. I had to have it! I figured it needed a starter. Anyway after all this time I finally put the motor on the boat last month, hook everything up. pull the plugs,hook up compression gauge, try to turn it over and nothing. I took the starter apart there was corrosion. Figured I would use the starter off my84 100. different housing. Took all the parts out put into other housing put it on. The engine turns slow (battery is fully charged) compression never gets past 60 so I decide to pull the lower unit to see if the motor will turn over faster and do the impeller while Im at it. Try the turn it over again still slow and about 60 on another cylinder. Im thinking new starter? So I turned my attention to the lower unit. Pulled the impeller housing and its full of sand. I cleaned the sand out blew it with compressed air. Now Im thinking this motor may have overheated. Does it matter how fast the motor turns on a compression check?
 

Bass_boy7

Petty Officer 2nd Class
Joined
Jan 18, 2008
Messages
161
Re: 1990 Johnson 120 has issues

yes it does matter if its turning slow you won't build up the proper compression or it could possibly be partially seized and is having a hard time try to turn over bc the pistons are scraping the cylinders just my guess i am not a mechanic, also double check your battery it could be pooched although"fully charged" it just may not be
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: 1990 Johnson 120 has issues

Always do your compression check with all of the spark plugs removed. Be sure to ground the sytem by pulling your kill switch lanyard.
 

QUIC

Cadet
Joined
Jul 30, 2010
Messages
14
Re: 1990 Johnson 120 has issues

thanks for responding. I had put some penetrating oil (pb blaster) in the spark plug holes yesterday and today the motor turned over faster and the compression is up to about 120 on all cylinders. is there anything I should be concerned about it maybe over heating?
 

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: 1990 Johnson 120 has issues

Since you already have the lower unit off go ahead and put a pump kit in it. Put it all back togeather and see how the cooling system is operating.
 

QUIC

Cadet
Joined
Jul 30, 2010
Messages
14
Re: 1990 Johnson 120 has issues

Hi everybody, finally got the pump kit in and lower unit back on. Tried to start it, very weak spark at first shot some ether in the spark plug holes nothing played with the gas ball took the plugs out tested weak again. shot ether in the holes again. tried tofire it vrrroom ran for a second now it has no spark at all. Any ideas guys? What should I do next?
 

QUIC

Cadet
Joined
Jul 30, 2010
Messages
14
Re: 1990 Johnson 120 has issues

Is there any real difference in the model years 1989 thru 1991 120 Im asking about buying a manual I can get a deal on a 91 oem manual and a deal on a 1989 parts manual
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: 1990 Johnson 120 has issues

The 1991 Factory Service manual should be fine.

The parts manuals are on-line so there is not much demand.
 

bananaboater

Ensign
Joined
Jul 27, 2009
Messages
932
Re: 1990 Johnson 120 has issues

Hey QUIC,

Saw on another thread you have a SC Jet and you were watching lakelover's restore. I have a Jet as well and you might like to see how I went about restoring mine. Two things I did not do, painting and transom (not really needed) but just about everything else.

If you get some pics and post them on the SC page or restoration page so we can see what you have that would be great. I always like to see other Jets regardless of condition.
 

QUIC

Cadet
Joined
Jul 30, 2010
Messages
14
Re: 1990 Johnson 120 has issues

Yes Bananaboater I will get some picks up of the jet It is a little rough but it has a story. I think I may have seen some of your resto, Do you go by the name Bananabert on another forum?
Quic
 
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