1986 Pontiac Firebird Trans Am Won't Start but turns over any ideas?

One day it just wouldn't start, no warning, weird noises etc. Messed around with it, pumping the gas etc and it finally started up ran a little rough and then smoothed out. The next time I went to crank it up it started right up. It has been fine for 2 months and now it did it again yesterday. Same thing, messed around pumping gas etc and it finally started and then today it won't start again. I have replaced the battery, spark plugs, wires, distributor and fuel filter. Any ideas? It is a 305 5.0L 1986 Firebird Trans Am Carb. motor