Engine revs high!!!!

[brothere]

Hi, I have a 1985 Johnson 15 HP boat motor on and 1978 alumicraft 15' fishing boat. I have just restored the boat and have run it a couple times....I am new to boats so this may or may not be a dumb question. I run the boat and I come accross times that the engine revs really high...the prop stops and motor is still in gear. This happens while I am moving (of course). I know the prop stops because the boat slows as if I let off the throttle but exhaust blows out like normal...My conclusion is that it does this because of weeds...is there some sort of mechanism inside the prop or gearbox that allows the prop to momentarilly disengage when it gets weeds tangled in it? If so, is there a way to adjust it so it doesn't do this for every little weed it comes accross? thanks a lot for all your help!!!!

 

[Jack Shellac]

Re: Engine revs high!!!!

Welcome to the forum. It sounds like your prop is spinning on the hub. The hub is the rubber piece inside the prop that fits on the driveshaft. The rubber hub is designed to absorb shock and sometimes the prop becomes loose on it. It's a press fit and there is no way to tighten it. Put the motor in gear, while it is OFF, and see if you can turn the prop by hand on the hub. You really need a torque fixture to do this right, but very few outside the dealer shop have them. The minimum slip torque on this motor is 100 ft-lbs. If it's loose, the solution is to re-hub or get a new prop. Good luck.

 

[brothere]

Re: Engine revs high!!!!

thanks for the insanely quick response!!! I just knew this wasn't suppose to happen with the prop but some idiot told me it was ok. The reason why I believed him was because every time it happened I was in the weeds and every time I stopped right after it happened, I checked the prop for weeds and there were some wrapped around it...I would simple put it in reverse for about 10 feet or simpley pick them off by hand. Right after that, I Had no problems with it until I hit the weeds again. So, he was right and wrong...it was because of the weeds but it isn't suppose to do that...right? How much would this cost to fix? Is it ok to run it like that for a while? thanks a lot again

 

[voodoo]

Re: Engine revs high!!!!

It is probably cavitation.<br />Weeds screw up the flow of water to the prop and allow it to run in an air space.<br />Remove the weeds and off you go.

 

[brothere]

Re: Engine revs high!!!!

AWESOME!!! I was thinking that it may be something like that...thanks a lot for saving me some money...was just about to go buy a new prop....I'm going to run the boat in water that has very few weeds and see if it still does it...I noticed that it does that when I turn sharp at higher speeds too...thanks a bunch!!!

 

[rwise]

Re: Engine revs high!!!!

brothere<br />pull the prop off and (on the back side) put a mark with a marker (waterproof) accross the hub and prop. put it back on and run it, then pull it, if mark is line up no prob, if not its spun!

 

[brothere]

Re: Engine revs high!!!!

hey...that is an awesome idea rwise...thanks a lot...I'll do that and if it has spun, I will replace the hub or the whole prop...found a new one for around $50 (that isn't so bad)...but I hope it is only the fact that it is weeds causing cavitation...thanks a bunch