if your gas switch is set to reserve (RES) then it saves gas by only using the left engine/pipe. mine does the same. and it runs rough like that. it may look like its on GAS ON. but the long end should be down. just a suggestion. hope you find out the answer.

 

haha i got a shee the other day and got on it started up second kick idled fine then took off on it and it felt like it was running on one piston so i hope your right about the reserve cause thats what i had the gas on and its to cold for me to pull the carbs off lol

 

If you put new reeds in the reason it is backfiring is because you need to rejet the carbs.also adjust air screws .aftermarket reeds on banshee are a big upgrade should also do k&n filters and pipe to go with it to make jetting easier.

 

Running your banshee on reserve will not cause it to run on one cylinder the only thing different is it pulls fuel from a lower point on the tank.