EVINRUDE 1980 70hp racing up while traveling problem

[BHOOKER]

I have a 1980 70hp Evinrude outboard that idles fine and with the cover off I can goose all 3 carbs and it almost screams and idles fine with my finger off the carb linkage.
I did gap (.030) and put in all 3 new plugs and a new gas line with no filter, with all new gas.
Here's the problem: with the boat in the water I take off and at about 10 or 15 mph the motor goes into a high raceing mode as if it slipped into nuetral but when I slack off on the throtle and give it gas the boat speeds back up some times up to about 15mph but after 50ft the engine races back up.
I thought maybe the prop gears or prop shaft was damaged so I took the prop completely off All teeth on shaft and in prop are fine.
While traveling on the water there is no gear grinding sounds at all.
I also drained the lower unit and put in fresh new gear lube.
The only way I can keep the boat moving on the water is by slacking off on the throtle (when it starts racing high) and slowly give it gas then the prop seems to have power. After 100 yards or so, same thing.
Man I really would APPRECIATE any advice or help.
Happy Holidys to all and thank you!!
Ben

 

[Barnacle_Bill]

Re: EVINRUDE 1980 70hp racing up while traveling problem

You have a spun hub. You can verify this by putting marks opposite each other on the inner and outer parts of the props hub. Try it again until it revs up like its been doing then check the marks to see if the are still lined up.

 

[BHOOKER]

Re: EVINRUDE 1980 70hp racing up while traveling problem

Thank you!