74 Mercruiser 140 hp will rev up but not move faster than 2 mph

[EEOCRAM]

Took the boat out was cruising along fine. Stopped to fish a bit, started it up and it would not cruise, just go about 2 mph and do a lot of bubbling at the trim. It would rev up but not go above 2 mph. Had to drive back about 2 miles to the dock that way.What would cause it to all of a sudden not get up and go after a shut down. I gave it gas, would rev up do a lot of bubbling at the trim, but not go over 2 mph. I did notice some fluid floating on top of the water around the trim. Could not tell if it was gas or oil.

 

[Fishermark]

Re: 74 Mercruiser 140 hp will rev up but not move faster than 2 mph

Did it overheat during that trip back to the dock? If not, I would suspect a spun prop hub. If it did, I would suspect a bad / stripped coupler.

Having said that... neither would account for fluid in the water.

 

[Haut Medoc]

Re: 74 Mercruiser 140 hp will rev up but not move faster than 2 mph

My guess is that you spun your prop hub....
Put on your spare, (you have one right)?.....
If not, you should....
Anyway, to check it put a mark with what ever is suitable, (I use nail polish), 1 mark on the nut, 1 on the prop, run (rev)the engine in the water under load, if the marks no longer line up, then that is your problem....
Take it to the prop shop.....​

 

[Bondo]

Re: 74 Mercruiser 140 hp will rev up but not move faster than 2 mph

I did notice some fluid floating on top of the water around the trim. Could not tell if it was gas or oil.

Ayuh,....

You probably otta figure out What that is,+ where it's coming from.....

 

[EEOCRAM]

Re: 74 Mercruiser 140 hp will rev up but not move faster than 2 mph

If the coupler was stripped would I have been able to make it back under idle speed?

This ismy first boat had it less than a week. Will get a spare now that I know this can happen, once I check for spun hub. I believe that is the problem after visiting local boat shop and talking to the mech.

 

[Don S]

Re: 74 Mercruiser 140 hp will rev up but not move faster than 2 mph

If the splines were stripped out, no, you would have been dead in the water, plus you would have overheated as the drive shaft for the pump wouldn't be turning.
If the rubber seperated around the splined sleeve in the couple, it would act just like a spun coupler and you would be able to go slowly. Normally when you speed them up and the slip like that, you can smell the rubber burning.

 

[EEOCRAM]

Re: 74 Mercruiser 140 hp will rev up but not move faster than 2 mph

I didn't smell any rubber burning so hopefully I'm good there. Should I check for any other damages if it happens to be a spun hub?