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Discussion Starter · #1 ·
I have a 1978 Johnson "Seahorse" 8hp outboard, and she starts, but won't idle for long. I think it is just a dirty carb, but I was wondering if anyone knew where I could find a copy of the service manual.


Thanks,
Mike
 

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I go with Seloc. Common sense words in there. I built a Johnson 135 HP with no prior experience with outboards and found all the advice in there worthy. About $27 on Amazon.
 

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Discussion Starter · #6 ·
Yeah I have been using the leeroyshamblings website, it has been helpful but I wish the exploded view pictures were labeled.

Quick update: I made a fresh tank of fuel, replaced the spark plugs, cleaned the carb, and checked the fuel lines and fuel filter. It turns out that the piece that controlled the idle broke off, so I am going to try to find a replacement for that. But even when I manually control the idle it still stalls. Could it be a fuel mixture issue? Any thoughts?
 

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Are the spark plugs gapped properly?
 

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You say it won't idle for long - does it run at higher RPM's?
If so adjust the idle to where it will run.

Forgive me for asking the obvious - but you didn't mention them:

Is the choke released (not just in, but really, you might have a bad linkage).
Check the air filter (remove it and try).
 

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Assuming everything else is OK it sounds like it may be a mixture problem. If it idles smoothly and then just dies, it may be too lean. If it idles roughly with a fair amount of smoke, it may be too rich. On the many outboards and motorcycles I have had the sort of "one size fits all" setting was 1-1/2 turns out from being closed. At idle, richen it up until it starts to stumble a little then lean it out just enough to get rid of the stumble. I like them just a little on the rich side.

Paul T
 

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Plus one on the dirty carb. It would also help to know how LONG it will run before it dies. Could be junk in the bowl, blocking the idle jet after starting. If it runs for a few minutes, could be the float sticking.

I would start with the carb bowl drain (if it has one). With tank disconnected, and a small white cup placed beneath, remove the drain screw. It can be a tight squeeze to get a cup under the drain, but get something there, to see if you get any grit or gunk out. If it runs clean, remove the carb, disassemble and clean.
 

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Lots of good tips here. One other thing you can try is after it starts, see if squeezing the primer bulb keeps it running. If it does you might have a fuel pump problem.
 

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Discussion Starter · #13 ·
The engine is just unreliable. It doesn't start every time, but when it does it will idle for between 10 seconds to about 2 minutes. When I rev it up it runs longer.

I gapped the spark plugs, so thats not the problem. I cleaned the carb, so thats not the problem. Fuel lines are clear, and the bowl drains fine, so thats not the problem. It has spark, air, and fuel. What else could I be missing?
 

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Is the choke mechanism working properly??
 

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Possibly, the float level is incorrect? Or, weak fuel pump? Sounds like it is running out of fuel at low speeds? You might try a seperate tank or vessel of fuel with a seperate fuel line, with no squeeze ball in it, held above and directly to the carb. If that works, it could be the pump or the tank/hose system. 2 strokes love NEW plugs.

Paul T
 

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Discussion Starter · #17 ·
Yeah it could very well be the choke. The is the one thing I haven't checked yet. What is the best way to go about checking the choke mechanism? What should I be looking for?
 

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Yeah it could very well be the choke. The is the one thing I haven't checked yet. What is the best way to go about checking the choke mechanism? What should I be looking for?
With the breather cover off, activate the choke lever.. you should see the little damper plate actually move from mostly closed (choked) to off (wide open). These levers usually just hook into the choke arm, or snap on so it's possible it's come adrift.... but it is just one possibility left after what you say has been dealt with..
 

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That only leaves compression.
Agreed.

OMC Outboards are reliable and simple when you address the basic things, so something simple may still be wrong. I had a head gasket leak recently and behaved similarly due to introduction of water in the combustion chamber. Shine a flashlight in the spark plug hole looking for water droplets. On mine the tiny droplets showed on the spark plug and wouldn't burn with a match. You can get a pinhole leak in the plug wires. Very common under the hold down clamp. Judging by the tiny black burn mark my guess is for some time the motor still runs. One time a friend had what appeared fuel problems and after trying everything, he pull the built in tank and found a june bug had crawled in the vent. Another tough one was a friend had a rust hole in the tank suction line in his car. Ran great as long as the tank was full. Some quirky thing will be found and you'll have a great little motor.

Good luck!
 

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Discussion Starter · #20 ·
I finally caved and took it in to a local small engine repair shop. Turns out the carb was completely shot, and needed to be replaced. But at least now I will have a reliable engine. Thanks for all the tips and suggestions!
 
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