I think your carbs backfiring as described are only a symptom, and not a cause. I'd be thinking along the lines of something timing related. Timing chain, cam lobes, bad distributor, etc. You better start looking deeper before a bigger problem rears it's head.

I'm pretty sure you still have a ignition issue. I would look hard at the cap, rotor and wires (primary and secondary)

A good place to start would be to remove the coil wire from the coil and have someone spin the motor while holding the wire near it. If you have a good and sharp blue spark its further down the line. If it is lazy and yellow it is most likely high resistance in the wiring to the coil(fuzzy bulkhead connector, "green" wire harness, ect)

My guess is that you will have hot spark out of the coil. Don't disregard the plugs either. I've jumped in the car in the spring after a long winters nap and had the car misfire like nobodies business. Set of plugs later it's cured.

Good luck

I earlier suggested ignition wiring or ignition switch as a possibility. Assuming that ballast resister is ok, disconnect stock ignition wiring going into it and run a 16 gauge or heavier jumper wire to the ballast from the positive post of battery. Then drive car.

If no ballast, run jumper wire directly to coil positive,,,but not for long as can be hard on points.

This will eliminate any doubts or concerns that switch or wiring is cause.

You do have negative from coil going to distributor,,,not positive which goes toward ignition switch?

Check dist cap for cracks and ensure that wiring internal in dist that goes coil to points is all in order. Have you checked dwell.

How many inches of vacuum at idle? Certain of no consequental vacuum leaks?

How much initial advance of timing,,,,,with any vacuum advance disconnected when checked?

Spark plug wires all clean and well insulated,,,,with no cross firing? Run engine in the dark and have a look.

any news

Any older rubber fuel lines? They can get soft with time and alcohol and the fuel pump will suck them shut... or they get air leaks on the suction side as posted above. Check/replace rubber lines, especially on the suction side, would be easy/cheap.

Just because the points look good they can still be bad.I just went thru it with one of my tractors.Not a Hemi but still the same thing.Start cold and ran great.warm up and started to miss and lose power.New points and adjust and all fine.Rocky

anything new on the problem?

Paul I had a very similar problem with my 68H a while back chased everything. Turned out it was the crummy REPRO ballast resistor. If like me you wanted the original looking one you may have bought one of the repros available. When I took it of and looked at it the resistor wire was barely connected to the clips. I ended up soldering in a heavy gauge wire in place of the resistor wire. I have pertronics under the cap so I don't need a resistor wire. Man what a difference night a day! so if you have a China repro too take a good look at it.

Still running terrible either replaced or swapped following:
- Fuel filter and pick up (sock)
- coil
- Condenser
- Coil wire to distributor
- Cap and rotor

Verified or checked operation of the following:
- points
- carb choke
- Timing
- did not see any arching between wires (ran in the dark)
- checked fuel push rod measured 3 3/8's
- New Fuel
- checked timing

The car was running great up until this time.... The ballast and ignition wire (dated 1972)were NOS when they were installed 10 years ago. Have not checked neither. Have not checked the resistance in the other coil wires yet.

Really appreciate everyone's help on this

Pull you carb lids and check your floats, see if either have a sunk float or a bad needle & seat. I'd change the N&S's while in there for good measure and be SURE your float levels are to correct spec height. Check your fuel pressure as well.

Here is a tought: You put a different coil in it and it started acting up faster. That coil likely made a change in the system load and something heated up faster than before creating a too high resistance pulling the ignition feed down to the point where the spark starts to suffer.
A weak connection can cause this and so can the ballast resistor. The ballast developes more resistance as it gets hotter.
How many volts do you measure at coil + both cold and hot?

Lars

Ok, I know that I'm getting pretty old these day but know I'm starting to feel real dumb.... I have replaced points and set the gap to about 0.017 (don't have access to a dwell meter). Replaced ballast, hooked everything up now I'm not getting any spark? only 4.7v at the coil???

Well after replacing the points and ballast the car is running like it should. When I replaced the points I must have damaged the wire to the distributor from the coil... After seeing the new points the old points were definitely the root cause!!! see picture

Thanks for everyone's input.... learned a ton. Great Web site with a lot of knowledgeable folks!!!! thanks again.