1979 evinrude 140 hp high speed miss

Austindh

Cadet
Joined
Sep 12, 2016
Messages
9
I have a 79 evinrude 140 that's been sitting a while. Cranks and idles fine. Will rev to 5k on land and will neutral rev in water fine but under a load at 3k rpm engine will cut out on one bank. Thinking the right side. Engine will eventually die if not returned to idle. It does starts back up and idles with no problem. Electrical issue I think but not exactly sure what. The stator and rectifier ohms good and stator puts out 300+v on both sides. Rectifier diodes good. Haven't tested much else yet. Any other thoughts or sugestions would be appreciated.
 

interalian

Commander
Joined
Jul 23, 2009
Messages
2,105
Revving up in neutral doesn't prove the engine is running properly, and you are at risk of damaging it doing so. Idling fine and revving in neutral (muffs or water) can happen on less than 4 cylinders if you've lost spark on one. Test your spark will jump 7/16" when cranking to prove it. If you're down one cylinder, you lose a LOT of power (I know as I dropped a coil and it felt like I had half the engine). Test compression too - this one should be 125/hole or more.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Your engine has two identical power packs, one for each head. You can do your own test. Swap the two power packs. If the miss moves when the packs are swapped, likely you have a bad pack.
 

Austindh

Cadet
Joined
Sep 12, 2016
Messages
9
I tested the plug gap at 7/16 and there was intermittent to no fire at all on one bank. Would fire a plug but not anything over about a 5/16 gap. Swapped power packs and problem swapped sides. So gonna order another power pack soon. Thanks for the comments!
 
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