Thanks for the comments folks.
OK For the record, I get the joke now. Sorry I was dense and missed it. I know what Joe was saying. Also fuel for it is not an issue in the fallout world so I am not making it an issue in mine. Either it will run on flamer fuel (which is essentially a form of gasoline, ignore that fact that it likely has thickening agents in it that would make it unusable for gasoline engines, there is a fair amount of suspension of belief in order to play fallout type game to begin with) or it will run on one of the compact nuclear type sources that that are used for energy weapons. The bottom line is, please do not try and give me reasons why it is not practical. I am not looking for practical. I am looking to duplicate the Fallout game world and play a fun game with it.
And as for how good a weapon it would be...if it is or isn't does not matter. I don't care what it is designed for, if I am a crazed, drugged out gang member in a post apocalyptic setting, and i have the ability to ditch my lead pipe for a running chain saw, I am going to do it. And if I saw that same crazed gang member coming at me with a running chain saw, I am NOT going to want to be hit with that thing. And I will try and take him out before I shoot at the pool stick wielding ganger next to him. Now that all being said, my emphasis here is not trying to justify the use of a chain saw, but rather the stats on one. I do like the suggestion about a presence bonus, but not as the main advantage, rather as an adder.