Think I know but don't know y

[moses]

Alright got this freshly built s13 sr. Puttin some miles in for break in but keep running into problems. Current problem is keep burning up spark plugs ghost white.
First. Started backfiring on deceleration. Pulled plugs found leaky injector, replaced o-ring with spark plugs.
Second. Drive to friends house then to autozone to buy a timing light then home. Set timing which was way off (not even on the marks). Fixed, drive to friends and back, backfire again. Pull plugs and there all white as hell.
Third. Switch them out cause maybe it happened with bad timing. Drive a couple mile circle and pull plugs again because of backfire. White as hell.

Now my air fuel ratio gauge is reading lean then rich. Bounces all drive. Fuel pressure is at 43psi at idle. Tune and timing is good. My guess is fuel pump, but it doesn't explain backfire because backfire is unburned fuel. I'll change fuel filter too just because too (it has 300miles on it). I never hit more than 2lbs of boost which was on accident so nothing should be hurt. Im using NGK bkr7e spark plugs. Could that be it since I'm not getting into boost? What do you guys think?