Evinrude Outboard HELP

[Wittkopfishing]

I have a late 90's Evinrude 30 HP outboard that has been running like a top for the last couple years. I was on a fishing trip recently and during the third day of the trip, I was on plane and it seems like my engine was louder than normal. I didn't think much of it at first, but then after fishing for a bit I went to run again, and upon acceleration there is was noticeable pitch change. Seemed like as the boat would begin to come out of the hole, the pitch of the engine sound audibly dropped and got significantly louder. I attached a video below and you can hear the pitch change at about the 5 second mark.

 

I was hesitant to run it very hard and risk any damage, but it seemed to perform fine, other than the noise. I could get on plane and sustain top speed as normal... was just loud.

My assumption is that there is an exhaust issue (gasket or something leaking under pressure) but wanted to see if anyone has ever experienced this before I take it to a mechanic.

Any help would be appreciated.

 

[Way2slow]

I'll have to ponder over that one.  My first thought is the prop hub slipping but it almost sounds like it's something with the air silencer.  Have you had the cover off and listened to it?  Might want to pull the air silencer off and see if it's coming from the carbs and see if one of the carbs has more blowback than normal.  Back when I ran Boysen reeds, I had on of those break a small chip of the end, letting it blow back into the carb.  

That's one of those you almost have to be there in person to diagnose exactly where it's coming from.

[MickD]

Does this engine have a separate oil tank that is pumped by a diaphragm pump in the engine?  If yes, the diaphragm pump is notorious for failing and scoring cylinder walls.   I hope  that is not it, because if it is the damage is already done.

 

When mine failed this way the idle quality  and cold starting were screwed up also.

 

 

[Wittkopfishing]

7 hours ago, MickD said:

Does this engine have a separate oil tank that is pumped by a diaphragm pump in the engine?  If yes, the diaphragm pump is notorious for failing and scoring cylinder walls.   I hope  that is not it, because if it is the damage is already done.

 

When mine failed this way the idle quality  and cold starting were screwed up also.

 

 

No, it’s a two stroke and just uses mixed gas. 

[Way2slow]

If you can find a friend that has as prop that you can try, I would do that.  It just sounds too much like the prop is cavitating or the hub is slipping.    Most any of the 25 30 and maybe even a 40 with the same pitch should work.

 

I got the thinking, (that's scary) for what it's going to cost you to take it to a mechanic, I would sacrifice the cost of a new, cheap aluminum prop the size of yours.  If the shop tells you it's the prop, it's going to cost you double for what just sticking on on will cost.  The are going to charge full list for an OEM prop and the about the cost of the prop in labor.  Plus, it always pays to have a spare prop anyway if the new prop does not fix the problem.

It sure sounds like the motor is spinning up without enough load on it to me, which is what a spun hub will do.

 

One other thought, you haven't by any chance done anything to move or change the trim stop pin and have it trimmed out too much have you?

[Wittkopfishing]

On 8/21/2021 at 11:11 PM, Way2slow said:

If you can find a friend that has as prop that you can try, I would do that.  It just sounds too much like the prop is cavitating or the hub is slipping.    Most any of the 25 30 and maybe even a 40 with the same pitch should work.

 

I got the thinking, (that's scary) for what it's going to cost you to take it to a mechanic, I would sacrifice the cost of a new, cheap aluminum prop the size of yours.  If the shop tells you it's the prop, it's going to cost you double for what just sticking on on will cost.  The are going to charge full list for an OEM prop and the about the cost of the prop in labor.  Plus, it always pays to have a spare prop anyway if the new prop does not fix the problem.

It sure sounds like the motor is spinning up without enough load on it to me, which is what a spun hub will do.

 

One other thought, you haven't by any chance done anything to move or change the trim stop pin and have it trimmed out too much have you?

Thanks for the thoughts. I have a spare prop that I could test. I had a similar thought because I had been running my boat through some vegetation and thought there might be a bunch of weeds in the prop, but I pulled it off and wasn’t anything in there. I might as well switch over to my backup prop and just see what happens. 

 

On the trim, no I have a standard trim setting that I always use and hasn’t changed it between the last time the engine ran normal and now. 
 

I’ll recheck the prop this weekend. 

[Wittkopfishing]

On 8/21/2021 at 11:11 PM, Way2slow said:

If you can find a friend that has as prop that you can try, I would do that.  It just sounds too much like the prop is cavitating or the hub is slipping.    Most any of the 25 30 and maybe even a 40 with the same pitch should work.

 

I got the thinking, (that's scary) for what it's going to cost you to take it to a mechanic, I would sacrifice the cost of a new, cheap aluminum prop the size of yours.  If the shop tells you it's the prop, it's going to cost you double for what just sticking on on will cost.  The are going to charge full list for an OEM prop and the about the cost of the prop in labor.  Plus, it always pays to have a spare prop anyway if the new prop does not fix the problem.

It sure sounds like the motor is spinning up without enough load on it to me, which is what a spun hub will do.

 

One other thought, you haven't by any chance done anything to move or change the trim stop pin and have it trimmed out too much have you?

Update. I took the boat to the lake for the first time in a while today. I swapped out my existing prop for my backup. No luck, was still getting the same sound from the motor. Interestingly, I put the boat back on the trailer and when I gave it gas, the motor sounded totally normal, even with the cowling off. 

Not sure what to deduce from that, but it seems like the noise chance only happens when I’m actually running. 

[tracker01]

Ok, this will sound goofy so here it goes. I have a 25hp Yamaha tiller prop job in the rear of my 16’ Bass Tracker Grizzly tin bot. I had something vibrating at low rpm’s. Similar to your noise. It went away as I gave it gas. I tightens every bolt, screw, motor mounts, and any nock and cranked I could find.

Next trip out it was gone.

just say’in.

 

[Way2slow]

Well, that shot down my main theory.  My other ideas would almost require me having it in front of me.  You can take the cover off and the air silencer off and see if it gets noticeably louder, but if it does, there's still not much you can do about it without knowing a lot about them.