70 hp evinrude has a hicup

zabortnick

Seaman Apprentice
Joined
Jul 29, 2013
Messages
42
1978 70 hp evinrude model 70873c. motor runs fine a low rpm but at half throttle or more it stalls for a split second causing the motor to go slack then bang the transome. it happens realy fast and i couldnt see it actualy lose spark on my telster, but it seams to lose either spark or fuel to all 3 cylinders at once and then regain. like i said it happens realy fast and you would think you bumped a stump if it didnt keep doing it.. i suspect somthing in the generating system because i swaped out the rectifier and no change. everything from the rectifier down seems ok. not sure if this is a symptom of a ignition module going bad? also after i got off the lake with the boat and was talking to the fella about fuel, lines, spark and such he mentioned that his gas tank (plastic) realy expands alot and its tuff getting the cap off. so i told him to loosen the cap and try it and let me know ( may not be letting tank breath).. has a new gas line and i could find no other restrictions.

I anyone has ran across this before or has some suggestions pls let me know.. dont want to start replacing part till i find it.'
Thank you.
 

scooter79

Cadet
Joined
Aug 18, 2014
Messages
9
I had simular issue with my 2007 50hp mercury. The motor would only do that under 2200 rpms or so but at high rpms or WOT it ran fine, i thought the motor was going to jump off the back and sink to the bottom. I had to remove my fuel tank and clean the tank and the vent and replace all the fuel lines since the had junk in them, rebuild Carbs and replace the reeds and read block and fuel pump. I had cracks and a few chips in the reads and the block had a fracture in it. After replacing and rebuilding the motor runs better than it ever has. hope this helps some.
 

zabortnick

Seaman Apprentice
Joined
Jul 29, 2013
Messages
42
Thanks scooter, but you didnt identify what your prob was. I cleaned carbs and it has new fuel lines and tank. im thinking maybe generator system.
 

zabortnick

Seaman Apprentice
Joined
Jul 29, 2013
Messages
42
Ok, I dug deep into the manuals and a loss of spark to all 3 cylinders is most likely a bad stator. Even if it is intermitent. also it said if you have a honey like substance on your motor under the flywheel and possibly driping on the head or top of motor, Your stator is bad. that is packing resin that has melted and oozed from the stator. good luck Fellas
 
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