I had my exhaust break off and went got it fixed.

I had my exhaust break off and went got it fixed, drove it for about a hour and a half and parked it for two days and went to start it and it just turns over and won't start. The truck has a rebuild on it with about 60k miles, it ran awesome a little cold nature like most isuzus. I've changed the fuel pump, I was told it wasn't getting enough gas pressure. (Still the same thing) I've also made sure I got spark on each plug, and it sparks. (It sparks about every 3/5 rotations) I've checked the timing and every thing is good, all new belts and everything. I haven't checked the distributor and seen if its jumped time (not sure how). I pour gas into the carb and it will sputter for about 3 seconds and cut off and backfire through the carb. I mean I was always told a little bit of gas should keep a truck running for a minute or so, but not mine. Not sure if it's the carb needing a rebuild kit or what? I poured about a half of cup of gas into the carb bowl and it started but just stayed running for about 5 or 6 seconds and stopped.