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Johnson 8hp STILL not right, but someone offered a new idea I want to run by y'all

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bcontento

Contributing Member
1990 Johnson 8hp J8RESR

Here is the backstory if you care to read: http://www.marineengine.com/boat-fo...0-8hp-Johnson-idles-but-no-wide-open-throttle

I've basically done everything to this motor, but it's still not right. I was going to break down and take it to a shop. When I spoke to the guy, he didn't hesitate at my symptoms and said it's bad a crankshaft seal causing extreme lean conditions. Sounds plausible to me since I've never been able to get it to run even close to "right" without backing the needle valve WAY out (instead of the recommended 2 turns), but then, it just leads to extreme flooding.

Does this sound like a reasonable diagnosis? Is there a way to test this without pulling the top apart?

How difficult a task is replacing the crank seal? I've seen a couple of videos showing some suggestions on replacing it. Seems pretty doable.

thanks all for the continued help!
 
The top seal is easy to inspect.------Power head is removed and the bottom seal is part of the exhaust tuner / adapter.-----No need to take the block apart to replace the bottom seal.
 
I said that the seal was part of the tuner / adapter.----So yes it is # 78.-----And I said that the block does not need to come apart.
 
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I am very familiar with replacing these seals. Ethanol is the culprit. The top of my work bench holds many samples for my customers to examine. It is almost always the top seal that goes, why? Seems it's the combination of suspended alcohol particles floating around under the cowling. This also expedites the decay of insulating foam that is glued under many cowlings. Once this foam starts to break down it all must be removed or it will end up getting sucked into the intake. I am working on a 75 Johnson with exactly that problem now. The little 9.5 horsepowers which I call "stubbys" are very prone to this as well but it is most often the upper crankshaft seal on these that fail too. If you decide to change the upper seal contact this thread again and I will explain an easier way to remove the old seal.
 
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Thanks guys. I am definitely replacing the upper at least. I took the flywheel off to expose the shaft.

For the lower, the lower unit cones off and I can access it there, correct? Does it make sense to also do the seal and bring? 77, 78, 79?
 
bcontento said:
Thanks guys. I am definitely replacing the upper at least. I took the flywheel off to expose the shaft.

For the lower, the lower unit cones off and I can access it there, correct? Does it make sense to also do the seal and bring? 77, 78, 79?
Click to expand...

The lower seal isn't available on that parts page nor on Amazon. Any suggestions on where to get one?
 
What is good spark and compression. You have the UFI ignition module has that been tested, that is not the best design with a high failure rate. A leaking seal will usually cause a higher idle speed.
Just something to think about. I have to change the windshield in my truck now I think radical ethanol molecules broke it.
 
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Did you check spark at all throttle settings. The problem with that module is as you run through the throttle settings the wires wear through. This will cause the spark to be erratic.
 
I didn't use a spark meter but did try the gap jump through the throttle range. I also replaced the plug and could wires.

Is the ignition module the same thing as the power pack? Are you talking about the wires that come out of the module itself? Again, forgive my ignorance.
 
Yes the ignition module is the.power pak. On your motor it sits under the flywheel. It was a bad design and had a high failure rate.
 
Okay, here is a great way to change that upper seal. Cut and bend a piece of tin can, like a soup can and slide it inside the seal (between the seal and crankshaft) to protect the crankshaft. Next carefully drill a couple 1/8" holes directly across from each other through the center of the steel ring of the seal. You will have to center punch a small starter "divot" for each hole so your drill bit won't "walk" towards the crankshaft as you will be coming in at a slight angle......unless you have a special "sleeved down bit" like I use. Just "barely" get through the metal part of the seal and don't drill deeper into the viton or rubber part below the steel ring of that seal. Once you have two holes there, thread in a couple good quality sheet metal screws, or self tapping type screws......like you would use on a stovepipe. Then pry up on the heads with a flat screwdriver to remove the seal. It may sound like a big deal but the whole process takes about 5 minutes.
 
Thanks all. Tim, that's exactly the method I've seen videos on.. appreciate the info. The top seal should be here in a day or so. I can't find the bottom seal for sale anywhere though.

If that doesn't fix it, maybe the power pack is next
 
The old upper seal out without any issues and the new one installed. Put the flywheel back on and it fired up really nicely even after I turned needle valve in where it's supposed to be. It's dark out so I couldn't put the motor back on the boat to let it run in the water but I will tomorrow and see how it is. I'll get the timing light out at the same time and see how that looks.
 
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