backfiring, whats my problem?
 

okay so my 305 was backfiring through the carb, so jokingly i tell my dad, lets get a 350, that will fix it. to my surprise he comes home the next day with a 350, we built it this week, put it in this weekend. guess what, the car still backfires. the only thing that is the same from the old engine is the air cleaner, carb, ECM, wires, and raditor, stuff like that. so, what are the likely causes for backfiring from the things that arent changed, as those have to be what is causing the backfire seeing as i have a brand new long block...just in case it matters, goodwrench 350, heads from that, comp cam 262, edlebrock performer...and the pistons and crank from the goodwrench. thats my engine now. so any help would be cool. thanks

When does it backfire?

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"So many Mustangs, so little time..."
ICON Motorsports

at about 1200+, it seemed more random though, we didnt run it long though, didnt see any point in doing damage to my brand new engine. im pretty sure it was random though, cause my dad was reaching over to do something, and i hadnt changed speed, and it popped him in the arm. but yeah, 1200+

If it pops while idling or a little more rpm , might want to check and make sure the choke is properly adjusted. If it pops when you rev it and then let off the gas check for any exhaust leaks. By the way are you still running your stock distributor?

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"Rice burners are like tampons...Every pu$$y has to have one"
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat, just switched to 180* b/c of winter coming and going to college in the mts.
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

well, i am POSITIVE it is not an exhaust leak, the gas came right of the carb and hit my dad, as in through the primaries. and yeah its the sort of stock distributer, not stock for my engine but off of another camaro. might be timing though, we had the thing on sort of backwards and so the timing was way retarded, ill see tonight

okay heres my update after testing. it is running rich,it is trying to run at 85% EGR. obviously this is creating my rich condition, however the tech 1 read a constant "lean condition". i believe this could be attributed to the oxygen sensor. it had an invarying milivolt reading, likely the cause of the lean reading. also we have a miss, we think it is likely plug/plug wire related. so heres the plan, new O2 sensor, plug wires, and plugs, and a MC solenoid to boot, although that is likely not a cause. anyway, what do you guys think of my plan? any q's about the diagnosis?

I have had a couple of wires get burnt and that has caused backfiring.

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"Rice burners are like tampons...Every pu$$y has to have one"
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat, just switched to 180* b/c of winter coming and going to college in the mts.
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

oh yeah one other thing i thought interesting, 7 plugs were a nice tan color, but 1 plug was like pitch black, that mean anything to ya? that would likely be the cylinder the burnt wire would be on right?