1978 15hp Evinrude idle help...

jupiter934

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Apr 13, 2010
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15
Hello so I have a 1978 15hp that won't idle right. I bought it like this. It starts right up and runs good and even "idles" with the throttle advanced to start location. Once you twist the throttle down past start she dies. I have the "idle speed" stopper knob dialed in as fast as it will go but never even make contact with the stopper before it dies.have rebuilt the carb. Upon rebuilding the carb I found the slow speed needle to be slightly bent so I figured this was the issue. I replaced it with new part and still no idle? I have the slow speed needle backed out 2 turns from seated. Please help I'm at least $500 into this motor so im hoping to get it running right. Thanks ahead of time
 

racerone

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Dec 28, 2013
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Report the values of a compression test, that is where the trouble shooting starts on 2 stroke motors.
 

raczekp1

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Mar 30, 2010
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did you try to play with screw on carb cam folower?
but in general rule if compresion is les than 90 psi its difficult to catch idle
 

jupiter934

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Apr 13, 2010
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Like I said I just rebuilt the carb so I know it's clean and free of blockage. I also should have noted the motor has good even compression. I did play with the cam follower and actually think this might be my issue as the motor pretty much dies as the cam follower loses contact with the cam throttle control.
 
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racerone

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Does primer bulb go hard when you operate it ?----Have you checked the reed valves ?------Have you checked to see if it is indeed running on both cylinders ?
 

jupiter934

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Apr 13, 2010
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Does primer bulb go hard when you operate it ?----Have you checked the reed valves ?------Have you checked to see if it is indeed running on both cylinders ?
I have not checked the reed valves or that both cylinders at running. How does one check? I do easily get full throttle so I just assumed both cylinders are foreign that and it sounds like both are firing.
 

BoatingCop

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Aug 28, 2007
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The black idle adjustment knob on the port side of the motor sounds like its broken. Mine was taken off by the previous owner, so my idle adjustment is with my hand. If I turn it all the way until it stops the engine dies. You can replace the whole idle adjustment assembly if you want. It doesn't bother me though. I've just memorized where it idles at the correct RPM.
 

boobie

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Pull one spark plug at a time when it is running and see if you have a dead cylinder.
 

AlTn

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Mar 9, 2010
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look under the Top Secret Files at the beginning of the Forum read "Decarbing an Engine"...use that process and see if it helps your idle issue
 

bwkre

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Jul 11, 2010
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177
I've got a 76 9.9, very similar, and there is now way I can turn the tiller handle to idler as it would also die. Only because the tiller gears and linkages have worn over time. I can get it to idle, just not where the handle indicates it.

You need to define "idle". Are the rpm's slow enough to engage a gear? Will it troll nice and slow? If so, it sounds like it's working find, just a worn tiller.
Mine also had trouble returning to idle from wot. A small spring under the cowling attached to the advance arm from the tiller solved that problem.

So does the motor idle, just not in relationship to the handle? Could be wrong but just asking.
 

tomhath

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Dec 5, 2007
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I did play with the cam follower and actually think this might be my issue as the motor pretty much dies as the cam follower loses contact with the cam throttle control.

That's interesting. Either the idle circuit on the carburetor still isn't working correctly (dies when the throttle plate closes), or it's shutting the throttle too soon (spark is too advanced for the amount of fuel it gets at idle).

Have you verified that it has the proper spark plugs? That does matter. It might help if you can tighten or swap them so the open side of the electrode is pointing to the intake side of the cylinder.

All that said, I don't think the 15hp Evinrudes are known for being real good at low idle. The 9.9s (same powerhead, different carb) idle real nice.
 

jupiter934

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Apr 13, 2010
Messages
15
Thanks guys for the tips ive been too busy with Holiday crap to work on it but will report back soon. Motor does "idle" just dies when throttle plate closes
 
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