89 b2200 runs bad (sometimes???)

Hey guys, got a 89 b2200 mazda pickup. Need some help. it's a manual trans btw. Anyways, when i start the truck it either misses or backfires very faintly (i can't tell exactly which). So it has new cap rotor wires and plugs. When i pulled the plugs they were covered black. Which is just truck runnen rich. But when i get to hi 3 speed or low 4 speed and above and just keepen a steady speed i feel it start sputtering. But you give it gas and it drives thru it. I haven't put a fuel filter on it (i've only had it 3 weeks. Bought it for 3 bills running). So i am gonna throw a fuel filter on it and some berrymans and see what happens. Anyone got any other suggestions? I'm new to the mazda scene and need this thing to last another month or 2 untill my chevy is stockfloored. Thanks fellas!

replace ur fuel filter.. mine did the same thing. and if that doesnt help try adjusting the valves

After you put the fuel filter on it if it still does it see if you have all the smog shit on it? If not that might be your problem. If you take the smog off but don't get a weber it will miss and run like shit unless your giving it a lot of throttle. It most likely is in the carb not the valves check on the passenger side of the carb there should be adjusting screws with a rod blocking them so you cant adjust them if that rod has been removed i would suggest going to a junkyard and finding one that hasn't been tampered with those carbs are finicky if you adjust them a lot of times they will never run right.