1976 85 horse Johnson take of problem

[mtrs85]

I had the boat out on the lake and it started acting up if i take of slow i can get going about 10 mph and then its as if something slips the rpms go up but the boat slows, if you let up on the throttle and ease back into it slowly it will take off again but as soon as power is demanded it slips. any help and info would be great. thanks

 

[jtexas]

Re: 1976 85 horse Johnson take of problem

couple possibilities:
* Spun hub. The rubber hub in your propeller has lost its grip. any prop shop can press in a new hub, not too expensive. To determine if this is the case, paint or scribe a mark across the metal outer hub and rubber inner hub, take the boat out and run it in gear. If your marks still line up, the hub is ok. Might can do it on the ramp with the boat still on the trailer.

* Cavitation. motor is too high or part of the antiventilation plate is broke off allowing the propeller to draw in surface air, or the diffuser ring is broken or has something lodged in it, allowing exhaust gases to bleed into the prop blades. With air mixed in, the blades don't have enough water to push against. The engine has no load so it revs up.

a couple tiny pieces of gravel lodged in the diffuser ring is all it takes (don't ask me how I know)

 

[outlaw241]

Re: 1976 85 horse Johnson take of problem

sounds like a spun prop hub

 

[Challenger84]

Re: 1976 85 horse Johnson take of problem

You can check if it is a spun hub by marking the rubber part and the hub and taking it on the water and pull it back up and check if the marks still line up.
If not then you have a spun hub..
Hope that helps

 

[mtrs85]

Re: 1976 85 horse Johnson take of problem

thanks for the info. I just got a brand new prop a week ago that was the first time i had it out. would have never thought to check that. Thank you again i will post the results of what i find and not another question.

 

[Challenger84]

Re: 1976 85 horse Johnson take of problem

any updates?

 

[kenmyfam]

Re: 1976 85 horse Johnson take of problem

thanks for the info. I just got a brand new prop a week ago that was the first time i had it out. would have never thought to check that. Thank you again i will post the results of what i find and not another question.

Post all the questions you like. Are you running O.K. now ???

 

[basbalj288]

Re: 1976 85 horse Johnson take of problem

I have the same exact motor... just bought it used and put on my boat. Same problem you are describing. It would take off fine at low speeds and then bog down and not run right at half open throttle. My timing was out of whack about 8 Degrees so after tuning that up with a timing light ( I was scared at first because I had no idea how until reading this forum, was real easy actually) it ran beautifully in low mid and high speeds...might want to check it out after seeing if the prop is spun first...

 

[jtexas]

Re: 1976 85 horse Johnson take of problem

If your motor is in gear and revving up while the boat slows down, then your problem is with the prop, not the timing or anything else on the powerhead.

If your motor is bogging down, and RPMs are decreasing or staying the same when you want them to increase, the problem is on your powerhead, and not with the prop.

Completely different set of symptoms each with completely different causes.