7.5 Engine Revs hi but little thrust

cleanriver

Cadet
Joined
Oct 22, 2005
Messages
7
I have a 1979 merc 7.5 that I just took out of 7 years of storage. Cleaned the carbs and it runs great.

However, when I took it out on the water, it putted along fine at low throttle. Then when I increased the throttle, the engine revved high but I got no additional thrust.
It seemed like perhaps something in the gearbox is stripped and cant handle a load.

What does this sound like to you ?
If it means a new lower unit....Is that a difficult job ?

Many Thanks
John
 

Barnacle_Bill

Admiral
Joined
Feb 8, 2004
Messages
6,469
Re: 7.5 Engine Revs hi but little thrust

It may be that the hub has dry rotted from sitting so long. Make 2 marks opposite each other on the back of the prop. One on the inner hub and one on the outer. Then try it again. If the marks are not still lined up have the prop re-hubbed.
 
Joined
Jun 18, 2007
Messages
20
Re: 7.5 Engine Revs hi but little thrust

Check for a broken shear pin if the prop uses one. May be tight enough at idle to push it along but at higher throttle the shaft could be spinning inside the prop. Not sure if your motor has a pin but worth checking.
 
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