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1970 25 hp Johnson running WAY too rich (video)

J

JRigby

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I am at a loss at where to go from here. I've almost exhausted everything I can think of. I'm not a mechanic and don't have a lot of experience. I can be resourceful and follow directions when I need to though ;) . I got a 25R70E - 25hp Johnson Seahorse from a guy near me for a decent price. He told me that it probably just needed a rebuild on the carb :rolleyes: (yeah right). I really wanted it because I already have a matching 1970 6hp Seahorse family heirloom that runs like it's brand new. When I first got the 25 home I could get it to fire occasionally but not start.

Compression on the cylinders after a good cleaning with seafoam was 115 on both. Yay! Checked the spark plugs and they were both firing , but I discovered they were the wrong model. I checked all the cross-references and they were definitely not the right ones. Replaced the plugs with correct ones and got it to hit and sputter a little more.

Pulled the flywheel off. Condensers, Coils, and Wires checked good on the ohm meter. The points looked... weird. They looked almost new. I discovered they were the wrong set for this motor and were bent to achieve the gap. Replaced the points, set the gaps. Motor would now run a little bit, but very hard to start and smoking like crazy. Bottom spark plug was black and wet, top one was black and sooty.

New fuel pump. No more wet bottom plug. Still running crazy rich though.

I decided to make sure the water was flowing so I wouldn't overheat it. Gearcase was full of muck, so I fully cleaned it out and replaced the seals. The impeller was mostly together, just two fins broken off - replaced.

Rebuilt the carb. I took it fully apart and checked every passage. It was already very clean and the replaceable parts looked new. The only gunk I could find in it was just some mild debris behind the metal plugs. HOWEVER... I noticed that the hole in the old needle seat was larger than the one in my new sierra kit (18-7222).

I'm thinking that somebody cludged together parts without doing any research and something else may be the wrong part number. The carburetor is definitely used and in good shape, but I wonder if it was taken off another motor. I wonder if it has the wrong size jet in it. I don't know what else to do. The power head looks like it's never been opened, as far as I can tell. Any suggestions?

Videos!!!

 
Thermostat in place and not stuck open ?-----Perhaps throttle plate is opening too early.------Put more water in your test bucket.----Why does choke on motor not work ?
 
racerone said:
Thermostat in place and not stuck open ?-----Perhaps throttle plate is opening too early.------Put more water in your test bucket.----Why does choke on motor not work ?
Click to expand...

I'll pull the thermostat in a little while. I have a new one for it anyway. Choke does work.
 
Got the thermostat out tonight. I think it was the original. It was extra crusty and definitely stuck open. I swapped it with a new one just to be safe. :cool: I didn't get a chance to try and run it tonight because of family stuff. Will try it Thursday.

Regarding the throttle, I adjusted it so that it starts to open right at the mark on the cam throttle control, I think that's right. I'll go back to that section in the manual and look again.
 
timguy said:
So did you check the plug wires? A strange color like red, to me is a "red flag".
Click to expand...

I checked the plug wires. They are stranded (I guess). I don't know much about spark plug wire, but I would assume solid core wire should have a single, solid copper conductor. What I have looks like it has about 8 strands per wire. Thank you. I will get some solid core wires if that's what I need.
 
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Update: Thanks for the solid core plug wire suggestion. I'll figure out if I need some.

I adjusted the throttle to open much later and borrowed my dad's timing light. I also fixed the stuck low speed valve adjustment. It's now no longer running overly rich, but still running poorly. Timing is off. The pic shows about where it is firing. The cam position in the below pic is also where I now have it set to start opening.

Other than a bent crankshaft key, is there anything else that could cause timing to go off like that?

IMG_20211209_212502786.jpg

And here's a video of it running:
 
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If it is stranded copper, that is fine. To clarify, I should have said "stranded copper". Now I'll watch the video over a fresh cup of coffee.
 
That appears to be a lean sneeze.-----A much debated concept.-----Not a well understood concept.----Open low speed mixture screw 1/4 turn at a time and it might go away.
 
Excellent job on the video. I gotta figure out how you set it right to your post. You are a wise man. Have to ask my son how to do it. He is pretty good with this too. Racer is right there with you. With videos like this, good audio, he can probably fix anything. Yes, lean "sneeze". Looks like a good motor. Just dial in that low speed better. The barrel operation will make it difficult to get perfect. The problem with running in a barrel is that the motor does not get as fresh and clean of oxygenated air as it would out in the real world. Besides that the cowling is removed and that changes the oxygen accessibility as well. Oftentimes I supply fresh Air with a fan blowing across the front of the motor. This will get you pretty close. Now where are my donut holes?
 
The saga continues...

I opened up the gap on both points to 0.025 - timing is now perfectly centered. I got it to start running and started fiddling with the low speed thing. It stopped firing on the bottom cylinder. I pulled the top off (again) and started testing. I get no ohm reading across the bottom cylinder coil now. I knew I should have replaced the coils when I did the points... gotta go find some coils now, I guess.
 
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