Logo
FULL SITE MENU

1979 55HP Johnson lower unit problem

P

pdshmm6

New member
"My 1979 55HP Johnson runs fin

"My 1979 55HP Johnson runs fine. Except when I accelerate the boat only goes about 1/4 of the speed its supposed to be going. When I run the engine in neutral it revs right up. But when I go to full throttle while its in gear the boat literally goes nowhere. The prop is going around but I think its like a car transmission that's slipping, not fully engaged in gear. I don't know much about outboards but I'm learning. Since the lower end of the engine tranfers power to the prop is that the likely problem and what can be done to fix it? Thanks."
 
"If you think your getting sli

"If you think your getting slippage from the gearcase, check the ruber centre hub on the prop. It is designed to slip if impacted hard enough from an object. Once it has slipped it has to go into a prop shop for rebuild."
 
Someone already told me about

Someone already told me about the prop hub being spun so I replaced the prop. It still does the same thing.
 
"very unlikely that the gears

"very unlikely that the gears are slipping.
its in gear or its not,do you hear anything when this happens,there are no clutches involved/that is why the prop hub was mentioned,revving an outboard in neautral means nothing,there is no load on it.how was this running before the problem,or was it recently purchased.
check your spark/compression and fuel delivery
i am gussing but a wot you are not getting full rpm <maybe something in the range of 3500 +-"
 
"I have this engine on a 16ft

"I have this engine on a 16ft aluminum Mirrocraft
I went to Lake Raystown in Central PA and the boat ran great for a week. Fast as could be...
I trailered the boat and took it home. Four weeks later I left on another vacation to Black Lake in upstate NY. When I put the boat in the water it ran as I described. When I was told about the spun hub theory, I went to a Johnson dealer and bought a brand new prop right out of the box. It still does the same thing."
 
"If you have a dock near your

"If you have a dock near your home you can test for a dropped cylinder. Tie the boat (securely) to the dock, warm up the motor with hood off. Put in gear and bring up the throttle, with an insulted pair of plyers pull off 1 plug wire at a time and ground it to the block. Your looking for no change in how the engine runs. That clyinder is not working. If that happens check for spark on the dead cylinder. If there is good spark...it leans to a fuel problem on that carb."
 
or water in you fuel.........d

or water in you fuel.........do you have a water/fuel sep ?

have you rechecked your spark plugs?........how do they look?
 
"Wow! I hadn't considered

"Wow! I hadn't considered that it could be a spark problem. I guess when the engine is running in neutral its hard to pick something like that up because it appears to be running smoothly.
Dave, I ruled out a fuel problem because I put fuel stabilizer in every tankful to counteract the effects of ethanol. As I said it had been running great and only sat for four weeks between uses.
Rollie, I like your idea about anchoring to the dock but that's going to have to wait until the weather warms up a little. I'll re-check the plugs. Is there any way to check the coil/spark system while its running with earmuffs on to see if there is any defect or lack of spark? I know you're not supposed to run it in gear when its out of water but..... if necessary is it do-able?"
 
"I really appreciate your help

"I really appreciate your help on this, guys.
I guess the real good news here is that there is no problem with the lower unit. That would really stink."
 
"Rollie,
BTW, sometimes mispe

"Rollie,
BTW, sometimes mispelling can result in real chuckler. I can easily follow the advice from your last post because I guarantee you that I have insulted my pliers and every other tool in my toolbox many times! :)"
 
"lol, the stories if tools cou

"lol, the stories if tools could only tell. When you explained that you only get 1/4 speed..does the engine rev right up (like screaming) and still not going at speed...or does it seem sluggish or rough running like it is missing on a cylinder. Your engine is a 2 banger so I would think that it would run terrible under load if it lost 1 of those bangers."
 
Back
Top