backfire and bb's on tin roof

It's kind of difficult to read the plugs from the pictures. But from what I can see the porcelain is very white...which might mean you're a little lean. You'd have to post a better picture of the plugs (or plug) that is up close, before I could say for sure. I'm assuming you have the 30lbers because of the nitrous. With that Hollye Systemax kit...24lbers would be plenty. Or does the Holley kit recommend the 30lbers? What do you have your fuel pressure set at? What, if any fuel system upgrades have you done besides the 30# injectors?? Is this a dry system you're running?

I know I said this before...but if you run your nitrous again, make sure the timing is set at 8-10 degrees btdc. 12 is too much.

When is the last time you've changed your fuel filter?