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Hey guys.  

I picked up a used outboard and everything seemed ok on it. Started up looks clean.  Tested it at home and it runs fine but then after about 20 seconds it revs up super high in idle.   Almost like the throttle is opened up fully.  If I turn the throttle it will rev up a bit more.   Any thoughts on what it could be?   It's a 2000 8hp johnson

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I am not a mechanic but my suggestion would be that it may need the carb rebuilt. I own a 1992 8hp Johnson. It is a great trolling motor.

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Not sure if this You Tube video will help, the motor in it appears to be a few years older. Not sure how much they changed the carb over the years.  

 

Edited by Old Man

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Looked at a online parts diagram for the 2000 8hp Johnson. It looks to be the same model carb as in the video above.

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The only thing that makes sense to me is that something is loose and causing it to run extremely lean,  and that's not good.

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I’d check the idle screws and mixture screw on the carb first before assuming a seal leak.

 

Edited by Old Man

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Oldman. I owe you.   I guess the idle screw was turned all up.   Tried it quick without water and it sounded great.  Tomorrow I'll put it to the test in water. 

Thank you!! 

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17 minutes ago, super dave said:

Oldman. I owe you.   I guess the idle screw was turned all up.   Tried it quick without water and it sounded great.  Tomorrow I'll put it to the test in water. 

Thank you!! 

You’re welcome.

That was my first guess. The previous owner probably tinkered with it at one point.

 

Edited by Old Man

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2 hours ago, super dave said:

Oldman. I owe you.   I guess the idle screw was turned all up.   Tried it quick without water and it sounded great.  Tomorrow I'll put it to the test in water. 

Thank you!! 

Without water?  Were you at least using motor muffs?  If not, I would replace the impellor too.

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Thanks to all that replied.  Your advice is very appreciated.   I attached a vid of it running. It's a bit Smokey but I'm assuming that's the fogging oil.   It hesitates for a second at the end but that's the bare wires of the kill touching. 

Thank you again! 

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My bin is green but that’s what I use it for too

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