I have a 1985 yamaha 150 etlk and I'm having surging mostly in the mid range. It feels and sounds like a cylinder dropping intermittently, Around 39 to 4400 rpm, compression good did a resistance test on coils 2 failed and replaced them, change all the plugs and went through the carbs they where fine, it condition started suddenly when leaving the fishing spot to head home, idles perfect starts every time, I have a manual and I did complete the resistance test on the yamaha control box unit part # and only had resistance very close to spec on 2 wires. Basically infinit on all other, this is my first yamaha i really can't find Info on what this control box actually does?
