Car running funny any ideas?

My 86 Honda Accord seems to be missing something terrible. Has very little power and backfires quite a bit.....It was running great and stopped and got gas at the local station and parked it in the garage for the night...during the night the temps with wind chills dipped to -30. The next day on the way to work it kept sputtering and not wanting to go once I stopped and seemed to have no/little power. I bought some HEET and put it in at work, have now used 1/2 the tank of gas and still doing it...even when I try to start the car it seems like its not really firing, then will finally start......any ideas ?.....