Firing order/timing?

Gooday, I drive a 1991 fiat uno fire 1100cc with 273000km on the clock. The car is a very reliable car. But now when I start the car it turns normally but there is weird ka-dof and idles very roughly that the whole car shakes wildly and as soon as I press juice it backfires and then cuts out! I dunno if its firing order or timing. My boss says its my cambelt. Please if I can get help/advice with this first then my "donation" will follow shortly with my next question. Thanks. Baron.