I have an Evinrude E-TEC 75 Model 2010 E75DPLIS, SN 05267561 that runs rough and is also surges at WOT.
Last September at the end of a week of fishing in Canada the motor was surging about 300-500 RPM at WOT on the way back to camp. It ran fine all week, but only did this on the last day.
After getting home I filled with fresh gas and ran boat again, same issue surging at WOT.
Took to dealer and no codes, suggested running Evinrude fuel system/injector cleaner, which was done this spring.
Still having same issue, surges now about 200-400 RPM at WOT, but can not get RPM to >4500.
Have been running the same prop on the boat for the last 5 years and it used to run max 5200RPM at WOT.
Took back to dealer and he changed plugs becuase they were not changed at last 3 year service.
Now it runs very rough at 1500-1800RPM, misses, and when I get it to 4500RPM it will surge and my wife says it has a ticking sound, which I can't hear because I can't hear.
Waiting in line to have it looked at and am hoping for some advice.
For the first 5 years that I owned the motor it ran flwalessly until last fall when it started surging a the end of a week of fishing.
I always run the 2+4 in every tank at recommended rate and winterize when I store in a heated shop every year.
A little frustrated because it has been such a good motor since I purchased it and now it runs so poorly it cannot be used.
Surging is almost always a fuel delivery problem. It could be anything from a kinked or deteriorated fuel line to an air leak or a weak fuel pump or stale fuel deposits. You have to monitor the fuel pressures, look for air bubbles, and visually check everything fuel related. Change the filters also and sample the gasoline for contaminants.
A trained tech can check the fuel system out fairly quickly with the proper tools, a laptop, and a test run.