90 hp revving up on its own

[moonman]

Finally got my boat out yesterday. 1988 Johnson 90 hp V4. Started up well and idled nice. Got started out onto the lake and got past the breakwall and gave it some gas. As soon as I got past 10mph, the motor revved up like crazy like up to 5000 rpms and it almost felt like we weren't even moving. I backed off of the throttle, put it in neutral, checked to see if we had caught anything in prop....nothing. Started out again and the same thing happened as I got over 10mph, revved up to 5000 rpms and seemed like prop was slipping. We just limped along for a few minutes and I tilted the motor I trimmed the motor down a little more and all of a sudden everything was fine. Boat ran normal. Can positioning of the tilt or trim of the motor cause such a surge? That doesn't make sense to me. Anyone know what would cause your motor to rev up like that? We fished for about 4 hrs and motor ran beautiful on the 5 mile ride in.

 

[boobie]

Do you have any weeds in the area you were in ??

 

[moonman]

Boobie, There are not a lot of weeds in that area of Lake Erie. I was thinking that the hub might have spun on the prop, but I would think if that would have happened, the boat would not have made that 5 mile run back in.

 

[Bosunsmate]

Is the anticav plate level with the bottom of the hull?
Maybe with all the people in there it was bow down and stern high resulting in cavitating

 

[emdsapmgr]

Our lake has weeds in a few shallow areas, esp in the canals. When my pontoon goes thru there at slow speeds, the weeds tend to collect on the lower unit. When ready to speed up in the main body of the lake, the prop just ventilates. It's always weeds. I just put the engine in reverse, and rev it slightly. Weeds come off and I'm back to normal high speed operation.

 

[moonman]

I guess it could have been weeds. I have never had that happen though. Definitely wasn't that the bow was down since there was only two of us in the boat. Thanks for your help

 

[Fed]

Spun hub, trimming in made it easier to get on the plane.

 

[moonman]

Fed, So if that hub has spun on a prop, is it possible that it hit a spot and stopped spinning, and that is why I was able to run the boat? I just thought if the hub has spun, you wouldn't go anywhere.

 

[Fed]

Yes moonman I have driven home on many spun props.