1969 Johnson 25 hp (exhaust all of a sudden got loud)

[wabah58]

Crusing back to the launch pad sunday, at WOT, and all of a sudden the boat lunged a little, and the noise of the exhaust get a lot louder. Dept finder said 15' so I know I didn't hit run it on the bottom. I stopped motor and checked to see the prop, looked good, and checked to see if spark plug was coming out, they also looked good. I went to start it and it started right up, so I limped back at a real low speed. But the noise of the exhaust was twice as loud as it normally is. Any body have ideas what this could be?

 

[jonesg]

Re: 1969 Johnson 25 hp (exhaust all of a sudden got loud)

check the exhaust cover gasket on the side of the head.

 

[wabah58]

Re: 1969 Johnson 25 hp (exhaust all of a sudden got loud)

check the exhaust cover gasket on the side of the head.

Ok I'll do that, I do have the factory manual for it, but Im at work right now, Im not sure where that exhaust cover is, hopefully it will show it in the manual. Thanks.

 

[14ftgrumman]

Re: 1969 Johnson 25 hp (exhaust all of a sudden got loud)

Or possibly the power head to mid section. If it dies wth the cover on, that would be a good indicator of that.

 

[R.Johnson]

Re: 1969 Johnson 25 hp (exhaust all of a sudden got loud)

Inside the outer exhaust housing, there is a inner exhaust tube. That tube is made of quite thin cast aluminum. I have seen a number of these crack in two just below it's mounting plate. If it is broken in two, it will give the noise you discribe. You will need to lift the power head to get at this part. That is not difficult on that engine. If you have to replace this tube, look at the prop for damage causing a out of balance. This is many time's the cause of loose, or broken part's.

 

[wabah58]

Re: 1969 Johnson 25 hp (exhaust all of a sudden got loud)

Or possibly the power head to mid section. If it dies wth the cover on, that would be a good indicator of that.

Still idles fine with cover on, And pulled up on the trailer just fine. Loud though.

 

[wabah58]

Re: 1969 Johnson 25 hp (exhaust all of a sudden got loud)

Inside the outer exhaust housing, there is a inner exhaust tube. That tube is made of quite thin cast aluminum. I have seen a number of these crack in two just below it's mounting plate. If it is broken in two, it will give the noise you discribe. You will need to lift the power head to get at this part. That is not difficult on that engine. If you have to replace this tube, look at the prop for damage causing a out of balance. This is many time's the cause of loose, or broken part's.

I pulled the prop off this morning, just because I wanted to get my coffee can closer to the foot, when I drained the lower end oil. It looks ok, but It is a old motor. Still has good compression on the power head, so I went ahead and kept it, putting new carb kit, and points in it. I got a couple good trips out in it. So should I get my water can out, start it up spraying the edge of the exhaust cover to see if it's leaking there, it not leaking there pull the power head off? And will that exhaust tube come right out or is there something holding it in, besides the mounting plate you spoke of??

Thanks for all the replies.

 

[R.Johnson]

Re: 1969 Johnson 25 hp (exhaust all of a sudden got loud)

That inner tube is held in the outer exhaust housing with four 1/4" bolts'.

 

[coolguy147]

Re: 1969 Johnson 25 hp (exhaust all of a sudden got loud)

never heard of a problem like this

usually i this happens to me cause of the boat.

how did this happen? were u just going straigtaway no waves?

or were u turning hit a wave or turing then went straight etc etc if u were going straight and no waves then look into what they were doing

 

[wabah58]

Re: 1969 Johnson 25 hp (exhaust all of a sudden got loud)

never heard of a problem like this

usually i this happens to me cause of the boat.

how did this happen? were u just going straigtaway no waves?

or were u turning hit a wave or turing then went straight etc etc if u were going straight and no waves then look into what they were doing

Was just going down stream, straight, no waves. I don't drink so it wasn't a drunken endevor, lol. I can assure you though it did happen. I guess I just have bad luck.