Johnson 1975 15 HP many problems worth fixing???

[Boatist]

I have a 1975 15 HP short shaft rope start Johnson.<br />A little history: About 15 years ago motor overheated when the water pump wore and dropped down and the drive key fell out. When I notice it was hot I slowed down and it died. Since we were in fast moving water tried to restart but could hardly pull roap and it would not restart. After it cooled down it started ok but I feel has had a little less power since. After I fixed the water pump it still always started first or second pull until just recently. Last ten years have used it on a 21 foot boat for trolling and a Kicker for safety should main motor ever fail in ocean.<br />Problem 1: For last 5 years used only for trolling with 50 to one TCW3 oil has fouled one or both plugs once or twice a day. Thermostat was stuck open so I replaced and that helped but still fouls plugs once every couple of days. For the last two years have been using 75 to 1 oil mix and will run 3 or four days before I have to replace plugs. Useing a hotter plug Champ L90C (896) also tried a set of Cham QL16V (876M) but fouled fast.<br />Problem 2: For the last 2 years have trouble starting it early in morning. It will start by second pull and if I rev it as high as can go with out putting in gear untill it warms up then it is good all day. If I forget to rev it up or it dies before it gets warm it will not restart unless I pull plugs and let it air for 30 minutes or more. I think it is flooded and probably a float problem.<br />Problem 3: If I run it wide open it will bogg down and die in 15 seconds and I usually have to replace the plugs. I think this is probably the high speed jet in CARB.<br />Last does any know if possible to change rings without pulling power head??????

 

[Franki]

Re: Johnson 1975 15 HP many problems worth fixing???

Hi Boatist..<br /><br />It does sound like your overheat has taken alot/most of the tension from your rings..<br /><br />have you actually done a compression test??? I would do that before stressing about changing them.<br /><br />I don't think I have heard of any outboards that you can change rings without pulling the powerhead off, but its not that big a job anyway.. (specially on a small motor like a 15hp.)<br /><br />I'd definatly put a kit through the carb while you are at it, (or at least a strip and clean.)<br /><br />and if you are fouling up plugs, then I'd be decarbing as well..<br /><br />Oh and last thing, stop running it on 75:1 ot you won't have much to rebuild.. find the reason for the problem first. you are treating the symptom.<br /><br />regards<br /><br />Frank

 

[Boatist]

Re: Johnson 1975 15 HP many problems worth fixing???

Hello Franki<br />You may be right about running 75 to 1 oil mix. Before I did that I talked to the OMC factory rep at the San Francisco boat show and he said I could run 100 to one with no damage as long as I never open it up. He said direct inject motors run at 100 to 1 at trolling speeds then increase to 50 to 1 when wide open.

 

[Boatist]

Re: Johnson 1975 15 HP many problems worth fixing???

^

 

[FlyBoyMark]

Re: Johnson 1975 15 HP many problems worth fixing???

Some of these little omc engines have a raw fuel recirculation system of tiny little rubber hoses. Make sure they have not been removed or are clogged. Thier attach points are the lowest parts of each crank chamber and return unburnt oil and fuel to the induction system.<br />This will also cause loading up....

 

[Boatist]

Re: Johnson 1975 15 HP many problems worth fixing???

FlyBoyMark I have had the motor since new and done all the work on it and have not removed any hoses. Where are these hoeses under the power head??? I have not worked on this motor much lately because I was going to replace it with the Evinrude 15 HP 4 stroke but of course now they are not making it and do not want to buy from Evinrude unless they continue to make same motor From Bombardier. What ever I buy I will Keep it for a long time and need to know that parts will be around. Thanks for reply

 

[the machinist]

Re: Johnson 1975 15 HP many problems worth fixing???

I have a 1978 9.9 Johnson that I bought new, converted to 15 hp, which is basically the same as your 1975 except ignition. It was never abused. <br />The last 2 years if started fouling plugs & was getting hard to start. <br />Also there was unburned carbony black oil that come out the prop, upper rear exhaust holes , etc. <br /><br />I finally pulled it apart & the compression ring had lost most of it's tension.<br /><br />Rebuilt the motor & it runs fine now.

 

[Boatist]

Re: Johnson 1975 15 HP many problems worth fixing???

Hello Machinist and thanks for reply.<br />Yes our engines are almost the same. The 15 has a different carb, bigger high speed jet and bigger throat 9.9 .625 dia / 15 .875 dia. I am not sure what year but they also redesigned the head to help plug fouling. The ingition has changed 3 or four times. If I find the time I would like to put in new rings, I have had the head off and the cylinder walls are fine. My motor has been very good until last couple of years. This weekend I am going to put a new starter rope on and take the carb off and clean. How much work was it to pull the power head and put in new rings????? Must be a gasket kit for that.