I've got a 1967 18 HP evinrude fastwin motor I'm having issues with. It's run great but has always had a slight problem. At full throttle for tweaty seconds or so it starts to die down until the motor shuts off, just like if it weren't getting fuel. After it does this, it is hard to start. I've had a mechanic work on it and have had a full tune up and rebuilding of the carb. I've explained the problem to him and he says the only other thing it might be is the fuel pump. It's got great compression so Is this likely the problem? And if it is how hard is it to replace the fuel pump or put in one of the those rebuild kits?