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Backfire through Carb

JohnDizzy

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Jun 1, 2017
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Location
Concord, NC
I have a 1973 Charger SE project that originally had a 440 but at some point had a 1969 440 swapped in. When I got it it had sat for several years. We got it running but bad fuel had the carb all gummed up. I pulled the carb, had it rebuilt and just put it back on with new spark plugs, ballast resistor and high torque starter. Car has an Accelerated super coil and wires, electric water pump and fans. I filled the float bowls through the vent tubes and tried to start it. The car will start to crank but then backfires a fireball through the carb and leaves a small fire burning in the carb. This is outside of my experience level so any help or advice on how to move forward and get the car running would be appreciated. I have read forums saying to check vacuum advance or the colts at the ECU, which I would do just not sure how to do it.
 
I also changed out the gas tank and fuel pickup. Blew out the gas line, dumped in 5 gallons of fresh gas and added a 100 and 50 micron fuel filter. Clear fuel filter is not showing any gas yet so dont think that the mechanical fuel pump has had time to draw from the tank yet. The battery is roughly a year old and has a full charge.
 
Did you remove and replace the distributor at any time? Maybe it's 180 out.
 
I don't remember pulling the cap and definitely did not pull the distributor point. With the wires routed the way they are I think it would have been hard to rotate it 180 without things getting tangled up but I can try flipping the cap. What am I looking for with the rotor?
 
cross firing from one spark plug wire to another can occur if they are touching each other, or a cracked distributor, timing that is too late (retarded) can cause a backfire
 
carbon tracked distributor cap, incorrect firing order, very retarded ignition timing
 
I also changed out the gas tank and fuel pickup. Blew out the gas line, dumped in 5 gallons of fresh gas and added a 100 and 50 micron fuel filter. Clear fuel filter is not showing any gas yet so dont think that the mechanical fuel pump has had time to draw from the tank yet. The battery is roughly a year old and has a full charge.
You can unhook your coil wire and crank the motor to get fuel up to the carb... you don't have to do it continuously, crank it for four or five seconds at a time and then stop for a few seconds until gas gets to the carb. I agree with the guys here that distributor positioning or timing is usually the cause of carb backfires, but it can also be from the carb settings being out of whack for startup.. if the problem persists, you may want to pull the distributor, set the motor back at TDC and start the startup process from the beginning... That way you can be sure everything is correct. Report back what happens! We can help you get it going
 
Here's how to tell if you're 180* out:
1) Pull #1 spark plug (driver's side front)
2) Use a remote starter (ground the #1 plug wire to the engine) or have a friend turn the motor over CW (as viewed from the front bumper) with a breaker bar and a 1 1/4" socket on the crank bolt while you put your finger over the #1 plug hole in the head.
3) When the compression tries to blow your finger off the hole, watch the timing mark on the balancer; it should be approaching the TDC mark on the timing tab.
4) When the '0' timing mark on the balancer lines up with the '0' mark on the tab, stop; just being close is okay.
5) Before pulling the distributor cap, take a sharpie and mark the location of the #1 spark plug wire tower, on the body of the distributor; then pull the cap and see where the rotor is pointing. If the distributor is in correctly, the rotor will be pointing at the #1 plug tower in the cap, if it were on (also the mark you made on the distributor body). If the rotor is pointing the opposite way, toward #6 plug wire tower, the distributor is installed 180* out.
Questions? BTW, the rotor rotation is CCW and the firing order is 1-8-4-3-6-5-7-2.
 
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Thanks everyone for the ideas and advice. I will check the wires to make sure they are not touching, verify the cap is clean and not cracked and try Coloradodaves instructions for getting the motor to tdc and verify the rotor location (before I pull the cap). I will let everyone know how it goes.
 
You have alot of info here to go from but till then I think we all would like to see some pictures I know I would !
 
Its hard to get any good pictures in my garage but here are a couple from when I got it, the engine bay before the clean up and what it looks like now.

IMG_20180605_065357339.jpg IMG_20180604_184735549_LL.jpg IMG_2931.JPG IMG_2939.JPG IMG_2941.JPG
 
If it's an electric fuel pump you shouldn't need to crank the motor to prime the carb, just cycle the key on and off. You should be able to hear it.
You may need to crack the line loose on top while you are doing this to bleed the air out until it gets a prime.
 
I appreciate all of the help. I feel like an idiot but I had the wires for 5&7 switched. Changed them and she fired right up. There is a metal tick sound now on the driver side but I will tackle that another night.
 
Ya...stuff like switched wires makes you feel kinda lame but it's such a relief, when it's nothing serious...good luck on the next thing(think easy...exhaust leak? snug up those header bolts!)
 
If it turns out you have a leaking header gasket, bear in mind to drain the coolant if you have to remove the header bolts. (if you have studs installed forget about this)
There are a few, if not all, threaded holes that are drilled through into the coolant system.
So if you remove a bolt coolant will drain out.
 
I like to take a sharpie and number the wires at the distributor and at the plugs.
Don't really care what it looks like.
You'll likely never have two wires swapped again.
 
I did the same, swapped the #5 and #7.
Reason was is, that i have the spark plug wire brackets and routed the wires different then the sequence to route the wires better to prevent them to touch the header tubes....after several explosions in the exhaust i figured it out :)
 
That's the best part, i have them installed...on the distributor :)
 
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