Okay guys im at my wits end on this one.
the motor is a
400 with a edelbrock dp4b intake. 1406 carb
the larger summit cam Camshaft, 1-Bolt, Hydraulic Flat Tappet, Advertised Duration 282/292, Lift .465/.488, Mopar,
long tube headers. no clue tube size.
parts store wires and coils. champion plugs. i think
older electronic ignition box. i have no clue where to start looking .any ideas?

When does it backfire? Any certain speed or RPM?

Maybe one of the lobes went bad on the cam?

it was as idle and just a little bit above.

Uhhh... misfire? Bad plug? Wire? Cap? One or two wrong (hot) plugs accidentally installed? Carb loading up maybe dripping fuel into intake ports on that side? Usually when I have a backfire on one side its the carb dripping fuel from venturi boosters due to float too high or dirt in needle and seat.

If it's just a minor backfire, like a pop, pop, pop, it could be a header/exhaust leak.

it was doing it a lot worse with the holley on it yesterday so I'm thinking maybe an ignition problem.

Make sure #5 and #7 wires are on the correct plugs.....I've never done that to a car, but I did find where somebody else did it...

we just fired up my buddy's challenger, he swore the wires were right, we put it on a lift, took off the driver side from the header, wld go pow after 5seconds, we took down from the lift, i sd lets look again, we had the #5 and #7 crossed.

check plug wires for connection and if they are touching/burned on headers or manifolds

what they said. check for vac leaks also.

my 440 backfires out the driver side only.

but mine is an exhast leak at the rear of the driver exhast manifold.

bang all 3 gears at WOT and let all the way off with a snap,then wait a few seconds and bang like a shotgun. then maybe a couple more if I engine break it all the way down form the WOT blast.

I did a drive by of my buddys with it in 2nd and reved up, killed the key pump the throttle,hit the key and made everyone on the carport dive for cover.

sounds like a SHOTGUN BLAST every time.I have blown muffs apart fliping the key to pop it,but the glass packs are holding up for now.

could be the 3x18 echo tips that make the bang loud.

guess it could be because i just have headers with purple hornies bolted directly to them.
and i know this is going to sound dumb but the firing order is 1,8,4,3,6,5,7,2 isn't it

Yep that is right.Check it at both that is right at both ends.It can be right at the cap but switched at the plugs.

remeber dist goes CCW on fire order.

you can always do a comp test to rule out a burnt valve in a cyl also.

i did a little diagnostic work today and heres the even numbered plugs

odd

Those plugs are shot. throw in a new set & see if it straightens out. Is that wet oil or dry carbon?

So i cleaned the plugs up because they are fairly new. that old Holley just dumped tons of fuel on them. they cleaned up decent enough i put them back in.
Then i checked the cap and rotor which was practically new. i did notice some up in down play in the distributor, not sure if that's normal or not?
It seemed like when i started it it was running really good and not backfiring. I'm going to play with it a little bit more tomorrow and see

if you guys can bear my ugliness i did get a video of it running. what do you guys think? youtube

I'm probably going to get flamed for this, but, IMHO, get rid of the Champions. I've run Autolite copper plugs in my MOPARS since my first one, back in 1969. No issues with them, ever.

For your application, plug number 85. $1.60 at your friendly Autozone.

I've used 85s for over 25 yrs, but that carb looks to be

fouling the plugs..fix that first. May be float level or rich

idle mixture.

plugs look badly oil fouled, take a close look at intake manifold sealing. You could take the carb off and you may be able to detect oil in the plenum.