Mercruiser 4.3L RPM's climbing by itself...

[bcnul8tr]

So I have a 2 year old 4.3L Mercruiser Alpha 4V on my 1991 Thompson with a Alpha 1 Gen2 Outdrive. We took the boat out today, brought it up to about 2500 rpms, and it went fine for about 5 seconds, and then the rpm's started to climb to almost 4000 rpm, the engine got a lot louder, but there was no power increase in the boat? I shut the motor down, thinking maybe my prop fell off or something like that but it was still there. Restarted the engine again, drove along at about 2200 rpms and it was fine, but when I brought it up to around 2500 again, the same thing started happening RPM's began climbing again. I took it back to the dock, and put it in Neutral and it was fine running at 2500 rpms in Neutral no issues, it seems like it was only doing it with a load... Any ideas on what the problem could be?

Thanks,
Miles

 

[Bt Doctur]

sounds like a slipping propeller hub

 

[bcnul8tr]

I didn't know they could do that, I thought once they went they just went. I thought maybe the engine coupler but I am not sure how to determine which it could be?

 

[Scott Danforth]

could be either a prop hub or coupling. both rely on rubber bonding. start with marking the prop and hub, then seing if the marks change with respect to each other.

 

[bcnul8tr]

I have a spare prop maybe i will try that in the morning first. If there is no slippage than it would be the prop right? I hope to heck it is the prop, it would cost me a fortune. The funny thing is the engine is brand-new well with maybe 60 hours on it, and the prop is the same age as well, 4 blade SS Solas.

 

[Bondo]

I have a spare prop maybe i will try that in the morning first. If there is no slippage than it would be the prop right? I hope to heck it is the prop, it would cost me a fortune. The funny thing is the engine is brand-new well with maybe 60 hours on it, and the prop is the same age as well, 4 blade SS Solas.

Ayuh,.... Are ya runnin' through Weeds,..??..??

Next time it does it,...
Shift to neutral, then a quick pump into reverse, with abit of rpms, back to neutral, then Go,....