HORRIBLE backfire issue

[MustangAndy]

Need help here guys. has happened twice today and now I'm seriously concerned about the car.

1971 Charger - base model
318 V8 (all stock - no speed parts) - new plugs (champion coppers), new spark wires, new cap, new rotor, new balast resistor. new air filter, new fuel pump, new fuel filter, freshly rebuilt Carter 2bbl. carb, fresh 87 gas.

Got the car fired up and running. sat at idle for about 10 mins. got in put the car in gear just barely touched the gas - BOOM!!!! - huge backfire. Smoke starts pouring out from under the hood. Open the hood to find the backfire was so violent it blew the vacuum canister off the passenger valve cover. Let the car sit for a few hours. Came back got it going -

Gear
Gas
Stall
Start
Gear
Gas
Some distance
Stall
Start
Gear
Gas
Some distance
Stall

Repeat about 10 times. Said "screw it". tied a tire to the front of my truck had my buddy get in and start the car to steer it while i pushed it with the truck to where I wanted the car out of the way. Stalled out on him. waited a minute then tried to start it. - BOOM!!!! - second time. Smoke everywhere and vacuum canister off again. had him muscle the steering the rest of the way into the pop up shed.

Any ideas as to what I should do or what the issue may be?

 

[1badgtx]

timing chain,distributor
Petty Blue 67 gTx

 

[shorty64]

...new plug wires indexed correctly vs rotor pointed at #1 cap terminal at TDC? More than once, I hate to admit, I've messed up the new wires positioning or firing order and got some really great backfires.

Good luck - always frustrating to tune one up and have more problems than before with the old stuff! Been there, done that, got the T-shirt!

 

[Patrick]

Replace the coil and fix the problem. While your at it make sure the wiring connection at the firewall going inside is clean and tight. If this fails replace the timing chain. I'm assuming you re-checked your plug wires and made sure its wired right.

 

[moperformance]

when was the last time it ran right? has it ever ran right. what has changed since then?

 

[greenmonsta79]

Did you adjust the carburetor properly??? sounds lean.

 

[70Fish]

In addition to the above, it's possible some of the new parts were defective so I'd also check that all the new wires are getting spark to the plugs.

 

[MustangAndy]

timing chain,distributor
Petty Blue 67 gTx

Please not the chain.

...new plug wires indexed correctly vs rotor pointed at #1 cap terminal at TDC? More than once, I hate to admit, I've messed up the new wires positioning or firing order and got some really great backfires.

Good luck - always frustrating to tune one up and have more problems than before with the old stuff! Been there, done that, got the T-shirt!

Did the wires one at a time and verified them against my Haynes manual.

Replace the coil and fix the problem. While your at it make sure the wiring connection at the firewall going inside is clean and tight. If this fails replace the timing chain. I'm assuming you re-checked your plug wires and made sure its wired right.

Coil is new as well. Recently pulled all the harnesses and overhauled them. checked for broken connections and rewrapped.

when was the last time it ran right? has it ever ran right. what has changed since then?

About 2 months ago was the last it ran. hasn't been sitting that long. nothing has changed outside of the weather.

Did you adjust the carburetor properly??? sounds lean.

Please to direct me to the newbie's guide for carb tuning. it's been rebuilt recently and my dad and I monkied with the screws a bit.

In addition to the above, it's possible some of the new parts were defective so I'd also check that all the new wires are getting spark to the plugs.

Will do.



_

 

[5wndwcpe]

Make sure the wires aren't cross-firing.

 

[oxytousc]

Yeah, I'd check the carb tuning. If it was recently rebuilt and you haven't dialed it in that will do it for sure. You can probably google around and find a good guide on tuning that carter.

 

[Ron 73]

Andy, If your prone to lots of humidity where your at and the car ran before without any problem, check under your distributor cap. Maybe there is some moisture that got in there, just something else you may want to check. Good luck.

 

[howiedodat]

He stated the car ran for about ten minutes, so I will assume it ran smoothly at idle. (if I'm wrong about that, start with the dist. set it to number 1 TDC and go thru everything from the dist to the plugs making SURE its not the spark). I dont know about the 2 barrel accellerator pump, but check to see if any fuel is being spayed into the carb when the thottle is applied. (car off, breather off). Like the brother said, it may be VERY lean and only running on the idle circut. It may be that it goes to lean once the thottle is opened.

 

[1badgtx]

Well,whats up with your car?Find the problem yet?
Petty blue 67 gTx

 

[1971RR]

From your post I'm assuming it idled somewhat smoothly for that 10 minutes and it backfired when you applied throttle. Is the vacuum advance hose hooked up? Is it hooked up to the right port on the carb? Was the distributor bumped/turned during the tuneup? And on getting the wires crossed, I had a Dakota that needed an engine requiblt. Took it to a local shop. Everything went ine until they tried to start/run the motor. They had my truck for 9 MONTHS!! Couldnt figure out why it would not run. I asked if I could have it for a couple days to dink around on it myself. Three hours later it was running great! Problem? They musta thought they were working on a Ford because they had wired the distributor starting on the #2 cylinder!! I reset the distributor and rewired it and it ran great. Moral of the story? I'm a genius? Not even close. I just started with the basics. Even professionals make the little mistakes from time to time and it takes a fresh set of eyeballs to see the obvious sometimes. (BTW, I paid for the rebuilt engine. But I did not pay for ANY labor on the whole job). Take your time, be patient and you WILL find the problem. Use the force if you have too...

 

[MustangAndy]

pulled all 8 plugs a short while ago. rear 2 on the passenger side were fouled with some substance. honestly feels like metal shavings.

wires check out ok. no moisture in the dist. and the retaining bolt is super tight. I'll play more tomorrow night.

As for idle - yes its smooth per say. still runs a bit high and sometimes it seems like the car has a lumpy cam installed. but once it settles down its all good. has a nice tick on the passenger side. think I'll pour a tiny bit extra oil in on that side. which raises another question. what weight do these cars like best?

 

[1badgtx]

Keep us posted andy!!!
Petty Blue 67 gTx

 

[condor74]

First things first. When you move the accelerator with the engine off, does the accel pump squirt fuel into the throat of the carburetor. If not then you have a problem with your accelerator pump circuit or clogged passage in your carburetor. If yes then start vehicle and let idle. Are there any vacume leaks? If so repair them. If not check ignition timing. It should be before top dead center. Look at your service manual for specs. I would imagine it would be between 5 and 10 degrees before top dead center. Here is the one thing to watch out for. If you harmonic balancer has started to come apart, the timing marks will no longer be correct. Adjust the timing by twisting the timing counter clockwise. This will advance the timing. Adjust it a few degrees at a time. If the throttle response gets better then it may have been timing.

 

[MustangAndy]

Um.........Noticed something new today. The oil is rather thin and smells like gas. What does that mean?

 

[greenmonsta79]

how much blowby does it have take the oil fill cap off the valve cover and see if it is blowing out the fill hole while running, rings could be shot, time for a compression test.

 

[condor74]

A more likely cause for the oil in gas problem and could also cause your fuel starvation issue is ruptured fuel pump diaphragm. If you are still using the the stock style mechanical fuel pump, replace it with a new one. Change the oil and filter before you run it. Also a good indication of the fuel leaking from the fuel pump is if the oil level is overfilled.