1969 115hp Johnson Idles very roughly, cuts out when increase the throttle

[pckeen]

Hi,

Just bought a 1969 115hp Johnson with a similar year boat. The boat is in fabulous shape, so I'm going to keep it. I was going to sell the motor and put a new one on, but when I removed the cover, the motor looks brand new. I have run it, but it idles very roughly and is hard to start. I was eventually able to get it going, and it ran well at speed for about 15 minutes. I then idled the boat for a few minutes, increased the throttle, and it died. The boat then would idle very roughly, and whenever I tried to increase the throttle, it died.

All I know is that the ECM (brainbox) was very recently replaced on the motor, and it seems that new sparkplugs, and I would guess from the appearance, new wiring to the sparkplugs was put on.

I'm a newbie to boat maintenance. Any advice would be appreciated.

Peter

 

[86 century]

Re: 1969 115hp Johnson Idles very roughly, cuts out when increase the throttle

That one has points under the flywheel so I would start by checking those out.
Next would be the carbs and fuel pump they are easy to clean think you can get the rebuild kits right here

 

[rockyrude]

Re: 1969 115hp Johnson Idles very roughly, cuts out when increase the throttle

Sorry, but that motor has the trigger sensor under the flywheel. If you haven't done it , a carb rebuild is first. Stuff gets caked in the passages when motors sit a while causing all kinds of grief. Make sure to replace the water pump impeller before you take it out again. Parts are available right here.

 

[pckeen]

Re: 1969 115hp Johnson Idles very roughly, cuts out when increase the throttle

OK - so I took a look at the motor, and did some reading.....and decided to get someone who knew what they were doing to fix it. Carb jets have now been opened up and examined - the mechanic says they looked pretty clean, but he cleaned the jets out to be safe. I opened up the fuel filter - it looked like new. Turns out I mixed the gas wrong, so a proper mix took care of the problems....

Boat ran great for 30 minutes - then the same set of problems again. It ran really rough, lots of vibration, a couple of what sounded like backfires, with the boat shutting down immediately afterwards. I was able to get the boat in gear, and run it for very low speed for a while. Did this for about half an hour or so, having to restart the boat every few minutes, then hey presto, the engine gives a little shake and it ran perfectly again for a while.

Any suggestions as to what could be causing this? Because of the age of the motor, I'm not going to keep taking it into the mechanics.

 

[rockyrude]

Re: 1969 115hp Johnson Idles very roughly, cuts out when increase the throttle

On mine, I found that the two wires going from the power pack up along the timing arm and under the flywheel to the trigger were shorting under the hold down on the timing arm. It's old and the insulation gets brittle, with the arm movement the insulation broke and shorted the trigger out.

 

[boobie]

Re: 1969 115hp Johnson Idles very roughly, cuts out when increase the throttle

Check your spark with a 3/8" open air gap spark tester and see what you get when it quits.