I have a 1983 suzuki lt125 and put a universal mikuni fuel pump on and it ran fine , then a day later it started to backfire and choke, checked the the gas tank and was just about empty . I filled the tank up and it still did it.
I took the spark plug out and closed the gap to about .025 and .026 from the suggested .027 and it throttled up fine. If the gap is bigger than .026 it will cut out and pop at accelleration what does this mean, could there be a coil or cdi problem.

 

What color is the spark? I would think coil problem, or something ignition related causing the spark to be weak.