mazda b2000 with 2200 engine

my truck is not firing on cylinder 3 new wires new plugs new button the carb was just and i was wondering if that would cause that problem i got a new webber 38/38 carb i ordered just to remove all the vacuum lines and i was also wondering what can i do to add hp that is kinda cheap just little tricks to get the most out of what i got

the old carb is crap i mean

Run a compression test to rule out a burned valve.