1976 25hp Evinrude tune up questions

imtawd77

Seaman
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Mar 5, 2005
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63
Hi, I recently purchased a 76 Evinrude 35hp outboard. It has been sitting unused for around 3 years due to a water pump failure. I fixed the pump, and noticed that one cylinder had little compression. I figured out the head gasket blew, so I replaced and both cylinders have great compression now... My questions are<br /><br />1 what is the fuel/oil ratio? 50:1?<br />2 How many turns out should the idle<br /> air/fuel mixture be turned out?<br />3 This engine likes to studder and buck <br /> around at idle... Would this be from the<br /> air/fuel setting being wrong? <br /><br />Thank you all for your help!!
 

JB

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Mar 25, 2001
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45,907
Re: 1976 25hp Evinrude tune up questions

Howdy, Tawd.<br /><br />Welcome to iboats. :) <br /><br />1. Yes. 50:1<br />2. Start with 1-1/2 turns out from seated.<br />3. That is normal when cold. If she does it warm the idle is a bit too lean.<br /><br />Get yourself a Repair Manual.<br /><br />Good luck. :)
 

imtawd77

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Mar 5, 2005
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Re: 1976 25hp Evinrude tune up questions

Hi JB, thanks for the reply. Is the idle mixture screw the screw that has the rich/lean knob sticking out of the front of the engine? If so, that one is turned out quite a few more turns than 1 1/2 and it has to be turned out that far to get rid of some of the studdering. If that is the wrong mixture screw, let me know. Thanks alot!!
 

reka12

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Feb 25, 2005
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Re: 1976 25hp Evinrude tune up questions

ImTawd: I have a '70 25hp and what you describe is the idle screw. On mine, the manual says to lightly seat the screw and back out one turn. Replace the linkage and adjust from there. On mine, I had to go to a hotter plug. It seemed to help a lot. Mike
 

imtawd77

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Mar 5, 2005
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Re: 1976 25hp Evinrude tune up questions

Great, thanks for the help. Does anyone know what the NGK part number is for the proper plug for this engine? Thanks!!
 

imtawd77

Seaman
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Mar 5, 2005
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Re: 1976 25hp Evinrude tune up questions

Oh Yeah, I mixed the gas at 42:1 just to be safe as I was not sure of the proper mixture. Would that cause the studdering at an idle as there is too much oil? Thanks
 

imtawd77

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Re: 1976 25hp Evinrude tune up questions

anyone know if that mixture would cause it to idle rough? Thanks
 

Paul Moir

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Re: 1976 25hp Evinrude tune up questions

No, that won't cause a rough idle. If you have the idle out much more than 1 and 1/2 turns then likely the idle circuit in the carb is partly clogged. Time to pick up a manual or borrow one from the library, get some carb cleaner and a carb kit.
 

imtawd77

Seaman
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Mar 5, 2005
Messages
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Re: 1976 25hp Evinrude tune up questions

Sounds good. Thanks for the info Paul!
 

jts4u

Cadet
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Dec 20, 2004
Messages
9
Re: 1976 25hp Evinrude tune up questions

Hi i had a rough idleing 25hp that backfired aswell. That proved to be the timing 180 deg out of phase.<br />regs JTS4U
 
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