I had the same scenario on an Evinrude back in the day. It would idle just fine and once i put the throttle to it the motor would struggle and eventually die out. One thing i did was had my better half in the cockpit and i would go back and squeeze the bulb and the rude would want to run. I changed out the fuel line and bulb thinking air leak somewhere, turns out it was a bad fuel pump. Once i changed out the pump, she ran as good as a rude can all the way to the day i sold it.