completely stumped...83 4 eye 5.0

[Dean "FISH" Caves]

here it is in a nut shell, 83 5.0 HO, under load, (any amount) loss of power, backfires thru carb, very rough idle, sounds and feels like 1 or 2 dead cyl. ..new edelbrock 600 carb, new edelbrock performer, new edelbrock 2122 cam, block freshly tanked and line bored, crank ground and polished, stock heads and valve components, valves were ground and new seals and retainers, new duraspark distributor, new MSD street fire box and TFI type coil, MSD cap standard rotor and new plugs and 8 mm street fire wires, elec. fuel pump....HELP PLEASE!!

 

[FoxBodyMustangs]

here it is in a nut shell, 83 5.0 HO, under load, (any amount) loss of power, backfires thru carb, very rough idle, sounds and feels like 1 or 2 dead cyl. ..new edelbrock 600 carb, new edelbrock performer, new edelbrock 2122 cam, block freshly tanked and line bored, crank ground and polished, stock heads and valve components, valves were ground and new seals and retainers, new duraspark distributor, new MSD street fire box and TFI type coil, MSD cap standard rotor and new plugs and 8 mm street fire wires, elec. fuel pump....HELP PLEASE!!

Can you post pics of the Engine Bay maybe something we can visual see.. Wires in the right firing order? etc...

 

[broncojunkie]

Does it idle rough, too? You could pull spark plugs and see if you have a cylinder or two not firing. Or, pull plug wires one at a time while idling. If you pull one and the idle doesn't change, that's the cylinder your having a problem with.

That will get you started, anyway... narrowing it down.

If your problem isn't cylinder- specific, you'll know to look elsewhere. (timing, intake, etc).

Someone feel free to correct me here, but it has been my experience that usually a backfire through the carb indicates a timing issue. I know other things can cause it, but timing is probably the most common.

 

[Dean "FISH" Caves]

ive had the front of the motor apart 4 times, timing is on the mark, plug wires, HO firing order, intake is brand new, as is carb, distributor and streetfire ign. box, 1 and 2 cyl plugs pull wet, the rest dry, my compression is 130 to 140 in all cyl. all pistons have new cast rings. yes it idles rough. i will get pics of detailed engine bay asap. thank you in advance....

 

[broncojunkie]

You might also try a leak-down test.

 

[Blown347]

99% of the time backfiring is ignition related, usually timing. If you've pulled each wire individually while idling and the idle gets rough each time, then the next thing I would check is the harmonic balancer. Turn the motor to TDC on the compression stroke on #1 cylinder and make sure the balancer reads 0 on the timing pointer. If it doesn't, then the balancer is spun so your timing reading will appear to be correct on a timing gun and could be way off. Then the balancer needs to be replaced. While its at TDC pull the cap and ensure the rotor is pointing at the #1 cylinder on the distributor.

If all if the above checks out OK and seeing as you're compression is good the next things to check would be head gaskets and carb

 

[broncojunkie]

I'm wondering if this is how it ran after putting the motor together OR if it ran ok and then developed the problem after driving it for a while.