Mid 50's Johnson 25HP runs like crap. Advice needed

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Huntleybill
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Huntleybill » Wed May 16, 2018 9:38 pm

UPDATE:
I have attached pictures of the reeds. None of them were stuck. I see nothing wrong but please look and tell me if you see anything.
Also, I took the carb apart. As you can see the float looks new. BUT.. isn't there supposed to be a felt type washer around the jet? I don't have a parts manual for this motor so I am not sure.

Also, I went back and re-timed the motor using Franks "special tools" but there was no change in the way the motor ran.
so, now I am not sure where to go next.

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Steve D
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Steve D » Wed May 16, 2018 11:10 pm

Huntleybill wrote:UPDATE: isn't there supposed to be a felt type washer around the jet? I don't have a parts manual for this motor so I am not sure.

In a previous post it was mentioned "The first time it's listed in a parts catalog for an RD/Bigtwin is in 1961" but some use one anyways on earlier motors.
viewtopic.php?f=2&t=13554&start=10&hilit=nozzle+gasket#p71399
http://www.marineengine.com/newparts/pa ... OMC0307778
And I don't see a pin holding the float on.
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nozzlle gaskets.png
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The preacher says all my sins is warshed away, including that Piggly Wiggly I knocked over in Yazoo.

Huntleybill
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Huntleybill » Wed May 16, 2018 11:57 pm

There is a pin, I just took it out to inspect the needle and seat.

FrankR
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby FrankR » Thu May 17, 2018 7:29 am

Wonder why there is so much more smoke & soot in the lower chamber than the upper one?

fleetwin
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby fleetwin » Thu May 17, 2018 4:47 pm

FrankR wrote:Wonder why there is so much more smoke & soot in the lower chamber than the upper one?

Am wondering the same thing...Is this the cylinder that isn't firing?

Huntleybill
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Huntleybill » Thu May 17, 2018 9:29 pm

See video. They are both firing. One is not firing very well.

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Fisherman6
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Fisherman6 » Fri May 18, 2018 8:02 am

The top cylinder is the one that is firing erratically and running poorly. The bottom cylinder is running normally from what I see in the video. I'm still feeling like this is an ignition problem. Either a bad coil or condenser seems most likely to me. I'd start with a condenser since that is the easiest thing to swap. If no difference, try a new coil, and wire. One other thing, have you tried swapping the spark plugs from top to bottom to see if the problem follows the plug?

If none of those things do it, maybe check behind the exhaust cover and make sure it isn't sucking water into the top cylinder somewhere.

-Ben
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Huntleybill
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Huntleybill » Fri May 18, 2018 9:31 am

Thanks Ben: I have replaced the plugs with no luck. The coils, points, condensers and wires are new. But that does not mean they are good. I was going to start re-replacing the ignition parts next.

Just to clarify, how would checking behind the exhaust cover reveal water? Wouldn't the hot exhaust blow out or dry out any evidence if that were the case? Also, since compression is 110 on both cylinders, would that not rule out any cracks, blown gaskets, leaks etc?

FrankR
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby FrankR » Fri May 18, 2018 10:10 am

Water ingestion from the exhaust cover came to mind here too. But I didn't say anything---till now. Those motors had an aluminum baffle plate between the block and outer cover. They are known to develop pin holes, which allowed water to squirt into the exhaust ports. Normally discovered too late, after the powerhead is destroyed by rust.

Michael
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Michael » Fri May 18, 2018 2:36 pm

The one plug that is clean had me wondering if water was getting in there. Could drop the lower unit and run it briefly without any water and see if the running quality improves. If it does, you have a water leak somewhere, most likely through the exhaust baffle like Franks says.


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