76 Evinrude 70 hp surging and bogging

[march2]

Hi everyone

Hope someone can help me before I pull my hair out with this problem. I have a 76 Evinrude 70 hp which has run great for years now. It starts perfect, idles perfect, and when the engine is cold runs perfect at all speeds. Once hot (maybe 4 minutes at WOT) it starts to surge at mid throttle and bog down, if I throttle down to idle it settles down but then when I hit the throttle it bogs. Weird thing though is that it's really mostly at mid-range, if I throttle up to WOT it seems to smooth out and run much better. Seems like the problem is between abut 30-80% throttle maybe? New fuel tank, hose, bulb and when it's surging it make no difference if I squeeze the bulb. I checked the fuel filter screen, looks fine. I also tried spraying a full can of marine engine cleaner into the fogging port, just to see if it would help but the problem remains. Any suggestions? Does it sound like a carb problem? My skill level is pretty basic (although I replaced a starter on this thing!) but hope there's some simple things I can try myself.

Thanks for any suggestions, I really appreciate it, boating season is very short up here in Canada and I hope I can get this back on the water soon!!

Thanks Marc.

 

[pn]

look up bad coil.

 

[fireman57]

nope, not a coil. That year there is a service bulletin out to redrill the carbs and holes under the core plugs. Have done two of them and it works perfectly. I bet if you bump your primer/choke when it does this it will pick up and go.