Engine keeps reving at wot

[NC22]

I have a 1969 Johnson 25 hp motor. At WOT the engine revs up and down. It takes about 15-20 seconds before it starts to rev. At about half throttle the engine runs fine. When it starts to rev at wot I bring it down to half throttle and it levels out then I can go to wot for about 15-20 sec's again before it starts to rev again. Sometimes sooner. This happens all the time at wot, not just once in a while. I have new plugs, new gas, and I'm using Quicksilver oil (TC-W3) I run this at 50:1. I also am using 8 oz. of stabil per 6 gallons of gas. This engine runs great at trollings speeds and starts on 2-3 pulls. Does anyone have any ideas as to what the problem might be?

 

[AMD Rules]

Re: Engine keeps reving at wot

Spun prop hub? <br /><br />Where's the motor anti-ventilation plate in regards to the bottom of the boat?

 

[roscoe]

Re: Engine keeps reving at wot

By revving, do you mean the engine revs up and down with a pulsing? If so, clean and re-adjust all carb settings and put in a new fuel pump diaphram.

 

[NC22]

Re: Engine keeps reving at wot

Im pretty sure that the hub is not spun. I try to turn the prop when it is in gear and it is very hard to do, and when it does the motor turns over. Roscoe thats exactly what it does. I will try what you suggested and get back to you guys. AMD, Im not sure what an anti ventilation plate is. Here are a couple of pictures of the motor at the bottom of the boat. Thanks for your responces. http://www.imagestation.com/album/?id=2126060779

 

[NC22]

Re: Engine keeps reving at wot

Upon examining my motor a little closer I noticed that my plug wires had a wear rub on them. They were not rubbed all the way thru the outer layer, but maybe enough to cause the spark to escape some. I put some more insulation on them and taped them up a bit. Also I insulated the bar that guides the wires. I'm hoping this is the cause of my problems. The only time that my wires touch the guide bar is at WOT. Here are some pictures of my fix. I would still like info on the anti ventilation plate though. Do mine look like it is at the right level? http://www.imagestation.com/album/index.html?id=2126056040

 

[Paul Moir]

Re: Engine keeps reving at wot

That looks like it's at the correct level. Compared to other boats it appears a little low, but that was necessary on older OMC outboards to ensure the water pump primed properly. You can experiment with setting the engine higher for better performance but you must make sure that it pumps water at both idle and WOT.