problems 1977 mariner 28 outboard

[edward ragno]

Motor runs great. Goes into gear goes good at low rpm but when given full throttle does*not hardly move. I have already replaced the lower unit. Thinking that was the problem. But not sure now what it is.
The older unit started the same thing last summer. Someone said it could be the prop slipping. What can it be?

 

[galamb]

Could be the prop slipping.

The propeller is two components - the blades (on a ring) and a hub that attaches to the splines on the prop shaft.

Between the two (on a standard prop) is a rubber (sleeve).

It is designed that way to allow a little give should you ground the prop - the rubber will allow enough to let go so you don't chew up the gears.

Over time the rubber shrinks/cracks/rots and at higher rpms the "resistance" of the prop on the water is enough to allow it to slip the compromised rubber.

If you had the motor connected to a tachometer you would note the rpms increase but the boat goes "nowhere", which is a sure sign of the prop slipping.

Without the tach if you can "hear" the motor revving up when it goes nowhere, you can consider that your "ear tach"

Swap the prop - they are a lot cheaper than a lower unit - should have been your first "try"...