# I/O seems like slipping at higher rpm's



## FISHIN 2 (Feb 24, 2004)

Need some opinions on a I/O problem. When putting boat in gear, prop will push boat at LOW SPEED, when throttling up, as starting to push hard, seems like prop is slipping. We tightened prop nut as tight as feasable, put back in water and it still slips, just as power is coming up. We thought it might be the prop, pulled that prop, put on spare and the same thing, ok, thought maybe another bad prop. Took prop off a good boat, same thing. What's causing the slippage ? Ok at low rpm's, try to power up and seems to slip. Is their a gimble clutch or any type clutch to check out ? Need some input, anyone . Thanks in advance, Mike


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## Priority1 (Feb 5, 2006)

If a different prop didn't solve the problem you may have an engine coupler slipping. Did you smell rubber burning? I hope I'm wrong because the engine will have to be lifted to make the repair. Sometimes when the gimbal bearing isn't aligned with the coupler it will cause the coupler to wear out prematurely. Is this a Mercruiser??? 
Frank


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## FISHIN 2 (Feb 24, 2004)

Yes it's mercruiser. We didn't smell any rubber smell. When we started,the boat would seem to be ok at very low rpm's, then as we throttled up, as to start pushing a load harder , the engine would rev as like the prop was slipping, I would immediately shut the throttle down, the prop would push at very low rpm's. We tried throttling up again, the same thing. Tried to turn prop by hand and foot and would not slip at all either. solid one direction, would click going opposite direction. Three props, same scenario, same results. Mike


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## hotdamnman1 (Oct 4, 2006)

yes engine coupler rubber (engine off of course)put your hand at rear of engine and fell for burnt rubber of aluminum shavings the splines on the coupler may be just about gone


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## waterfoul (May 18, 2005)

can only be two things:

Prop hubs spinning. But 3 in a row leads me to number two

Coupler hub spinning. Shoot, until just a little while ago I had a spare coupler in the garage... but sold it to a guy I know. The beotch of it all is that you have to PULL the motor to replace the coupler. No simple task in most boats. Yank the drive, yank the motor. Not cheap unless you can do it yourself.


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## FishTales (Feb 13, 2002)

waterfoul said:


> can only be two things:
> 
> Prop hubs spinning. But 3 in a row leads me to number two
> 
> Coupler hub spinning.


Click on the link below, scroll down to find your engine and click "view part"
Rich
Mercruiser Drive Couplers


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## Hilljack (Mar 18, 2002)

Here's a great site I found when trying to help my friend diagnose the same problem.

http://mercstuff.com/spunprop.htm


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## Greenbush future (Sep 8, 2005)

Sometimes when I take off with my 115 Merc outboard and if the engine is trimmed up too much I get the same effect. Are you sure your outdrive is all the way down? Just an easy thought?


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## FISHIN 2 (Feb 24, 2004)

Thanks fella's, gonna see where this takes me. Hope it's not too bad of a job. Mike:yikes:


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## Sixshooter (Mar 16, 2003)

I would say first verify the prop hub hasn't spun. That is the cheapest thing to do. 

I spun two props in one summer...DOH...Of course both of them were very old so the rubber was dry rotted a bit. But I would check the prop rubber first. If you have a spare prop try that.


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## FISHIN 2 (Feb 24, 2004)

We have already tried the spare prop, it sounded the same. Thought maybe spare was bad, so we borrowed a prop off of a usable boat, did the same thing. Not that simple. Gonna check the coupler. Thanks, Mike


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## Duckman1 (Oct 14, 2004)

It may not be the coupler. I had a similar problem with my mercruiser I/O.

It would go along fine at low RPM then run it up on plane and it would start to rev up and fall back down. RPM's all over the place on the tach.

It turned out to be some electrical problems mostly due to needing electric ignition and plug wires. May want to have both coupler and rotor/ignition checked out.

Good luck!


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## waterfoul (May 18, 2005)

Hey, what year is this outdrive/boat/motor???


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## FISHIN 2 (Feb 24, 2004)

Boat is a 1970, CRUISER, 350 motor, mercruiser outdrive. Tach revved up and I shut it down, not giving it a chance to go up and down to answerd mans Q. It was a constant rpm. Thanks though. Mike


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