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 » Tue May 15, 2018 10:33 am

definitely smoke and not steam. I have a fan running right behind the motor blowing the smoke outside.

NJ-boatbuilder57
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby NJ-boatbuilder57 » Tue May 15, 2018 10:45 am

Is 100% of this coming out of the exhaust port?

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

Postby Jeff Register » Tue May 15, 2018 10:57 am

Had a 58 J. 35hp, went thru the fuel, shook at idle & once W.O. ran fine....broken reed. Where the missing metal went?
Frank hit the nail on the head,

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Garry in Tampa
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Garry in Tampa » Tue May 15, 2018 12:11 pm

Just looking at the plugs you can see one cylinder is running rich and the other lean. The compression readings would rule out a scored cylinder. I would think more it being a broken reed . . . :roll:
I had one come in with a complaint of leaking seal & rough idle. It turned out to be a hole poked in the crankcase by a loose nut. The hole was covered by the crankshaft counterweight during crankcase compression. He got a new powerhead under Evinrude's warrentee.
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Fisherman6
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Fisherman6 » Tue May 15, 2018 7:05 pm

FrankR wrote:I think you are barking up the wrong tree (carb tree). There is something wrong with that top cylinder. You claim the spark is not the issue, so look for something else. Crankcase sealing? Water getting into cylinder? Scored piston? Busted reed? But first double check the ignition.

The smoke is because the top cylinder is not burning its fuel, but is discharging it into the exhaust.


Frank said It! This is exactly what I was thinking when I watched your video. Something is causing the top cylinder to not fire / burn it's fuel properly. All that smoke is the unburned fuel mix from the top cylinder. I run my RD-16 on 16:1 often. The 16:1 mix alone is not making it smoke excessively. When you pull the top plug wire, it's running like it should (more or less) on the bottom cylinder. When the bottom plug wire, it is running pretty poorly and erratically on the top cylinder. My guess is its an ignition issue. If I were troubleshooting it, I would start there. It could be any of those things Frank mentioned though. It's definitely worth looking at the reeds.
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Huntleybill
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Huntleybill » Tue May 15, 2018 7:42 pm

OK...I will take it apart and look at the reeds. I ruled out the carb because of what happens when I pull the plug wires. I was second guessing it being an ignition issue because when I pulled the plug wire on the GOOD cylinder, it still ran (albeit crappy) which tells me it has spark and the ignition is good. I have no idea if my reasoning is accurate tho!!!

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

Postby Fisherman6 » Tue May 15, 2018 8:55 pm

When you pull the plug on the good cylinder it runs poorly, as you mentioned. That indicates it is sparking, but it does not mean the ignition is "good". I have had several motors run well on one cylinder and poorly on the other. It would be well enough to keep it running at full throttle or near that, but if you put neon spark testers inline with the plugs and run it with them, you should see your bad cylinder showing weak and/ or intermittent spark. That is assuming it is ignition and not induction. It's easy enough to check the reeds and rule them out. This issue has always been ignition for me, but reeds are certainly a possibility.
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Huntleybill
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Re: Mid 50's Johnson 25HP runs like crap. Advice needed

Postby Huntleybill » Tue May 15, 2018 10:58 pm

Hmmm I don't have neon spark testers. FANTASTIC, I can buy more tools! :-)
I'll try that.

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

Postby fleetwin » Tue May 15, 2018 11:23 pm

OK, watched the video but wondering why you are not attempting to adjust the low speed needle? I noticed that killing the top cylinder does not seem to affect it much...Is the tank pressurizing? Perhaps one of the rubber tank pressure valves in the manifold is messed up. Does it look like the intake manifold has been messed with?
I don't want to lead you down a bad path though. You might consider putting that engine on a boat and trying it first, before getting in too deep...

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

Postby Jerry Ahrens » Wed May 16, 2018 6:43 am

Don has a good point.I would try to run the engine full throttle, while tuning in the high speed needle till it leans way out. Then adjust it open till it runs smooth. If that works, THEN you can move on to the low speed needle adjustment. I noticed that you are moving back and forth between the high and low speed needles.... trying to adjust the carburetor that way won't work. Do the high speed needle first, before moving on to the low side. Having said that, I think you may also have a reed valve problem as well, or something else going on. If it were me, I'd try to adjust the carb properly first, before moving on. If your quick and on your toes, you can get that high speed needle adjusted fairly close in a test tank.... at least close enough to be able to adjust the low speed side
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