1985 Honda CRX

I have 2 questines one is it starts up fine and sounds good and revs good but when I give it gas it seems to lag no power then when I let up off gas it backfires from the rear and front I changed the sparkplugs and distributer cap and rotor it seemed to help it, could it be bad gas this problem didnt happen intil I filled my tank up at safeway gasstation in novato ca is that possible maybe I should drain the gas out of it and put fresh gas in 2 questine should u be able to turn fuel injecters by hand