engine won't idle! please help

i have a 66 with a 289 v8. i've never had any problems with the engine running before. i left it sitting for 3 months or more, and now it will start fine and run ok with some throttle, but won't idle (it kind of jumps between 700 and 50 rpm and then dies). could it be that the fuel has gone bad? any other ideas?
 
well i guess it had just been too long since i ran it, the carb must have been gummed up. i put in some fuel stabilizer and after an hour the surging was greatly decreased. after driving it around for a couple hours, its back to normal (so far). thanks for the help!