Hi, A few things you can check, first the dist. cap, look for carbon trails, check the rotor too. look for cracked or bad plug wires, firing order too.18436572. if that isnt it, check your valve lash,you may have a tight one. do a compression check, a burnt intake valve would give a constant pop. even a bent pushrod would do it. This is all a good place to start. there are alot of things to go wrong but these are the most common. Good luck
Well it could be numerous things, first check the timing, if the timing is somewhat off and it doesn't idle very good and backfires slightly, the timing chain may have jumped a tooth. Chevy small blocks are also notorious for flat cam lobes, this can be checked by removing the valve covers and checking the lift at the rockers when manually turning the engine over. However before checking any of this, start with the basics, check the manifold and carb for any major vacuum leaks. Vacuum leaks will cause a bad idle and also slight backfire at acceration. Did this condition happen all at once or gradually?, if it happened all at once, I would bet on a jumped timing chain. GOOD LUCK!