Losing Propeller Thrust

[wilberking]

I've got a 1966 Evinrude 9.5 HP which I bought used. Runs pretty well. I had it out a couple of weeks ago and had no issues. Had it out again yesterday with a heavier load in the boat; after running about for a bit at full throttle the prop thrust pratically disappeared and engine rev'ed up. I backed way off on the throttle to slow and prop thrust was fine. However as I tried to give it more throttle, engine would rev up again adn I'd lose thrust. I was able to move about fine at slow speed. Thoughts?

 

[hardwater fisherman]

Maybe your hub is spun on your prop. Make a mark from the center hub and the outer casing of the prop. Then run it until it slips again and then check to see if the mark still lines up. If not then the prop is spinning on its hub.

 

[wilberking]

Can I try this test in a water pail, or should I try it under similar conditions? I should mention that I lightened the load in the boat and it didnt take much throtle with just me in the boat to have the prop slip and lose thrust.

 

[hardwater fisherman]

Are you saying the motor revs up but you do not gain speed or do you just have no power? You might have to have the boat on the water with the motor under load to create the slippage.

 

[wilberking]

The motor revs up, but there's no acceleration or speed increase. I move along fine with the throttle set to slow. But when I increase the throttle, the engine rev's but there's no acceleration.

 

[Silvertip]

Very likely a spun hub. A prop shop can fix that but a new prop may cost about the same.

 

[Wolfe64]

This happened to me a few weeks ago
Spun prop

Mark

 

[Wolfe64]

With the motor out of the water and the cowl off I could spin the prop by Hand and the flywheel would spin but when it came up on compression the flywheel stopped turning but I could still spin the prop

 

[wilberking]

Can I confirm that it's a spun hub by removing propeller and inspecting?

 

[jakedaawg]

If it is bad enough sometimes the rubber in the hub will be twisted andntorn. Its not always evident to the eye though. I would have thought a motor that old would be a shear pin motor but i probably mistaken though. I dont mess with the old ones much.

 

[nwcove]

With the motor out of the water and the cowl off I could spin the prop by Hand and the flywheel would spin but when it came up on compression the flywheel stopped turning but I could still spin the prop

^^^ that is a dangerous thing to do. as mentioned, mark the prop and hub, run the motor under real conditions until the problem happens, then check the marks. more than likely a spun hub, but a slight chance that the motor may not be deep enough below your transom or just tilted wrong for the extra load.

 

[Wolfe64]

Why is that a dangerous thing to do? Nothing was running I was turning the prop by hand, when the motor came up on compression the motor stopped turning and the prop kept spinning............by hand

Mark

 

[Bobdag]

If the motor fired on the compression stroke you could lose some fingers. Unless you made sure the motor couldn't start. Like disconnecting the plug wires or disabling the ignition.

 

[Wolfe64]

Of course I made sure the motor wouldnt start. I did have the key off and plug wires disconnected.
My mistake I should have mentioned that in my other post.

Mark

 

[jakedaawg]

Thinking back, i am almost positive this is a shear pin prop. Pull the prop. The shear pin may be sheared and and catching just enough to run at idle.

If shear pin is good its time to check the lower unit fluid for signs of metal in the oil.

I just dont think they had small hubbed props in 1966.

 

[wilberking]

I think it's a shear pin issue, I have the owner's manual and it covers Drive Pin Replacement ( see link to photo) https://goo.gl/photos/edhRbDqQ3WgJcvAX6. So I guess it's not a "hubbed" prop. I'm a newbie with outboards. I was confused since I was getting thrust at low speed. I thought if it were the drive pin, I'd get zero thrust.

 

[interalian]

Still a rubber hub on that one IIRC. The drive pin is just that.

 

[hardwater fisherman]

I think it is possible for a prop with shear a pin to get spun. At least there is several threads on other sites that says it is.

 

[interalian]

This old ad from 1963 seems to imply there's a rubber "cushion" in these props.

 

[jakedaawg]

Great, i try to learn somethingneveryday