1977 Johnson 115 starting issues

[smokey173]

I have a 1977 Johnson 115hp outboard model #115EL77S that starts and runs beautifully when I use the muffs. When I launch the boat into the lake the engine will sometimes start but often not. It almost seems like the depth of the water has a bearing on it starting. Last time out the motor started after launching and I traveled across the lake to my favorite spot and shut it off. After an hour or so of fishing I went to start the motor and it just cranked and cranked until I started blowing the starter fuse. After being towed in I took it out of the water and BOOM..it started right up. I checked the compression and it is within specs and balance with the guidelines a dealership gave me. I heard later from a person with the same problems that the motor has to be tuned in the water and not just by the muffs. Is this true? If so, what exactly is the procedure for tuning? How do I check the timing? Thank you in advance!

 

[tashasdaddy]

Re: 1977 Johnson 115 starting issues

"It almost seems like the depth of the water has a bearing on it starting"
100% TRUE.

the exhaust exits thru the prop. when in the water the motor has to run fast enough to force the exhaust out the prop, this is called back pressure.

when on muffs, there is not any back pressure. thus, the engine does not have to work as hard to get rid of the exhaust.

solution: on muffs set your idle speed at 1,000 rpms. when the back pressure is added in the water, it should start. then you can fine tune you idle speed, in the water with the motor in gear.