Do you have a zombie escape plan? If not, you should. But there's a saying in the apocalyptic survival biz that we use when people run for the obvious weapon established by Ashley J. Williams of "Evil Dead": Don't be a Berkeley. Why? We'll let TVTropes explain:
While cool, there are good reasons the chainsaw is not exactly the first choice among melee weapons in the real world; chainsaws are heavy and hard to swing with any degree of finesse, have poor reach compared to their weight, require fuel or an external power source, make a lot of noise, and will tear through the person wielding them just as cheerfully as the intended victim... Chainsaws are also prone to a phenomenon called "kickback" where one tooth of the blade contacts something without cutting it and the resulting shock throws the blade backwards violently, often right at the unfortunate operator's head; obviously, this is all the more likely to happen when they're being used as a weapon. The chain also runs the danger of snapping and whipping the user in the process. Fictional chainsaws also have the ability to start instantly, with one pull of the starter handle, unlike in Real Life where they require several pulls and most models will need to warm up for at least 30 seconds or they'll immediately die when you try to cut something. Most Real Life chainsaws also dull in seconds if they touch anything harder than wood. Finally, running out of fuel or suffering a broken chain or clutch will leave the erstwhile chainsaw maniac holding a big, unwieldy and rather useless club.