Evinrude 40hp surging

[Heller1]

Got a 1986 evinrude 40hp that has been causing me all kinds of headaches! starts and idles fine, can get about 30% throttle and then the surging, erratic running and dying starts. So far, new fuel tank, fuel tank lines including ball, 2 fuel pumps, spark plugs, cdi, I cleaned carbs once, had carbs cleaned professionally once with the float set to spec. I have run out of ideas on what could be causing it. any help or ideas would be greatly appreciated!

 

[racerone]

Compression test needs to be done here.

 

[Heller1]

compression is 112 and 109

 

[fireman57]

I am guessing that you have had this engine and it used to run fine. If not then definitely check compression. If not the get a buddy and run it with the carb cover off and have him slowly close the choke plates as you are running and see if it picks up. If it does then it is starving for fuel, if it doesn't then you may have an air leak at a carb gasket or a fuel line.

 

[Heller1]

compression is fine. Yes, the motor ran fine until this summer. i can push the primer when surging and that doesnt help at all, so that might rule out air leak. All the fuel line has been replaced and carbs cleaned twice in my hunt for this issue. carb gasket has also been replaced twice. I am now wondering if it is an electric issue and not a fuel issue....thanks for the suggestions, gonna try everything i can at this point!

 

[fireman57]

When you push the primer does the engine slow like it is flooding or is there no change? You might run it with the cover off and make sure the butterflies are actually closing. Get a spark tester and make sure that your spark is jumping 7/16" and bright blue. Orange spark is not sufficient. If you have this on all cylinders then get a timing light from Harbor freight or wherever and put it on the plug wires one by one and make sure you have spark when you are throttling up. Again, this will require another person to be safe. Could have a bad coil and losing spark under a load.

 

[jakedaawg]

no coke butterflies on this model. When it is surging have someone continuously pump the bulb. If that helps look to the fuel pump.

 

[fireman57]

Jake you are right on the choke. he said he already put 2 fuel pumps on that is why I didn't suggest pumping the primer bulb. He also did not state if these were new or used fuel pumps.

 

[Heller1]

brand new fuel pumps. Everything pointed at fuel pump so I replaced. Then brough it to a shop and they replaced the fuel pump again. the bulb gets hard, pumping it did nothing either. I will check for spark next. thanks for all the tips!

 

[juno pierrat]

if you've got a manual id start checking charge coil and ignition sensor ohms and voltages, OR just remove flywheel and look for the dreaded black ooze under those parts.