'58 Evenrude cough/jerk when going above idle

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pjaymac

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May 15, 2007
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I have a 1958 Evenrude 18hp Fast Twin that has a cough/jerk every 5-10 seconds when going above idle. It runs strong and does not have this problem when idling or going real slow, but when speed is increased this occurs. I believe the low speed adjustment/mixture and high speed adjustment/mixture are adjusted properly. I have installed a carb kit; cleaned the fuel filter; adjusted the points; checked for leaks on the fuel system/gas tank. I have tried to get rid of the cough by changing high speed adjustment in small increments but it didn't work. I waited at least one minute between adjustment changes.

Any suggestions?
Thanks.
 
iwombat

iwombat

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Re: '58 Evenrude cough/jerk when going above idle

A cough every 5-10 seconds sounds more like an ignition problem to me. Might want to double-check your plug wires, grounds, and inspect the condition of your coils. Also, give that kill switch a look-see.
 
tashasdaddy

tashasdaddy

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Re: '58 Evenrude cough/jerk when going above idle

it's the old lean sneeze, rich cough of these older motors.
 
iwombat

iwombat

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Re: '58 Evenrude cough/jerk when going above idle

I would expect it to be much more frequent than every 5-10 seconds though. Maybe not.
 
Chinewalker

Chinewalker

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Re: '58 Evenrude cough/jerk when going above idle

Lean sneezes typically only happen at lower speeds. At higher speeds a lean condition will either result in a loss of performance or cooking a piston.

This sounds like either a cylinder cutting in and out, or possibly a bad clutch dog. The clutch dog would result in a severe shuddering of the motor - like you hit something...
- Scott
 
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F_R

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Re: '58 Evenrude cough/jerk when going above idle

Lean coughing happens at idle. Jumping at higher speeds is a clutch dog. Feels like you ran over something? Watch the gearshift handle when that happens, you will see it jump. What is happening is it is coming out of gear, rotating one half turn, and slamming back into gear. From your description, it is really worn out bad. You will need a new clutch dog and forward gear. Maybe some shift linkage repair too, from letting it go so long. Be prepared to dig deep in your pockets.
 
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pjaymac

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Re: '58 Evenrude cough/jerk when going above idle

Thanks so much for the information, even though it is bad news.
 
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