You know, the chainsaw isn't nearly as powerful with another class as it is with the berserker, which should be obvious.
And a berserker with a chainsaw is VERY vulnerable to certain enemies. This is where teamwork comes into play.
I think what we need to do, is find out just how long a chainsaw runs in real life, with the throttle held all the way down, with a full tank of gas. If the thing runs a good hour, or a half hour, or whatever, then it'd be reasonable to assume the chainsaw in the game wouldn't run out of fuel during a match.
I personally don't run around with the primary fire held down all the time, I only have it going when I need it. Shoot, half the time I don't even have it out, but rather, the knife, as I can't hear anything when the chainsaw is out.
I really don't think we need a timer, or fuel, or anything that restricts the use of the chainsaw. It would nerf a class, and I think that's the last thing we need. Lets make other classes better, not cripple one class. Especially since the class doesn't need any crippling. So it can tear through the weak mobs pretty easily, so can every other class. Scrakes are about the only stronger enemy that the berserker can take on easily, and he's the only class that can take him on without taking much damage.
On the flipside, the berserker is the one class that takes more damage than anyone(potentially at least. If they have a different target obviously the berserker isn't going to be hit.) against a fleshpounder or the patriarch.