Need Help with 78 Johnson 115hp motor

[pltrkt]

I just bought a pontoon boat with a 78 Johnson 115hp motor. I took it out on the lake today and I had a little trouble starting it (first time using this season) but once I got it going it ran pretty good at first. When I maxed the throttle the motor would run fine then it would almost act like it would skip a gear and just rev, and then it would push the boat along good again and then slip and rev.....it kept doing this so we backed off the throttle a little and it ran just fine. After about an hour or so of playing around on the lake we were heading back to the boat ramp and I dropped my wife off at the dock to back the trailer in the water. I put the boat in reverse and prepared to load the boat on the trailer. The boat stalled and I could not get it started again. When I turned the key the motor would not even attempt to turn over......... The motor was completely rebuilt in the fall of 2003 and was only put in the water once in 2004 (according to the previous owner). We put new gas in and bought a new battery. Can you tell me where to start looking for problems? I have never worked on a motor this big and would like to know where I should start hunting for the problems......and if there is anything I should do to ensure everything else is in working order before I attempt to take this boat onto the water again.<br />Thank you for your help

 

[DJ]

Re: Need Help with 78 Johnson 115hp motor

Is it seized?<br /><br />Can you rotate the flywheel by hand? Try it with the spark plugs out and battery disconnected.<br /><br />Let us know.

 

[pltrkt]

Re: Need Help with 78 Johnson 115hp motor

Yes I can turn it by hand fairly easily

 

[pltrkt]

Re: Need Help with 78 Johnson 115hp motor

I figured out the problem with the starter, the bendix is not engaging (this is richard's wife, he is out working on the boat right now so we can go fishing). He is now taking the lower unit off to check it out........do you have any idea why it would be bogging down when we max the throttle? Is there any other maintenence that we should do before we put the boat back into the water

 

[R.Johnson]

Re: Need Help with 78 Johnson 115hp motor

The slipping could be caused by a Spun hub in the prop! do you have a spare prop you could try? If the bendix is not engaging the flywheel, and since you have a new battery, check all of the connections. Don't use the wing nuts' that came with the battery, replace with stainless, or brass nuts'. Check the engine ground strap where it bolts to the block.

 

[Silvertip]

Re: Need Help with 78 Johnson 115hp motor

To check for a spun hub on the prop, place a mark anywhere on the hub. Then make another mark on the outer part of the prop directly in-line with the first mark. Then go for a ride and try to duplicate the splipping problem. When you get back check the marks. If they are still lined up the hub is not spun. If the marks are no longer in-line, the hub is spun and will need to be repaired.

 

[prolinews]

Re: Need Help with 78 Johnson 115hp motor

The prop also may be the wrong size if it is not a spun hub.A bass boat speed prop doesn't work well on a pontoon boat.

 

[Solittle]

Re: Need Help with 78 Johnson 115hp motor

If the prop is not the culpert the symptoms you describe could also be due to crud in the carbs.<br /><br />Don't let the size of the motor intimidate you.