Backfire thru exhaust at idle

[Smokinnjokin]

What voltage regulator are you running? Check voltage while idling, should be between 13.5-14.5 and not decrease after 5-10 minutes. When you rev the motor it should stay steady or only go slightly higher. The sign of a inoperative charging system is battery voltage at start, decreasing steadily as you run. This does not mean your alternator is bad, more likely voltage regulator inoperative. When running off battery voltage your ignition will be very weak and foul plugs at idle. Which can cause you to start chasing your tail with carb tuning. A solid state VR that looks like the factory one is readily available for cheap on eBay. Until you sort out charging, I would not touch anything on the carb.
-if you have verified that the charging system is working correctly, set your airscrews per edelbrock instructions using a vacuum gauge and with the car in Drive with parking brake set. This should solve your fouled plugs. You can also verify that the needles are staying down at idle by removing the covers while idling and physically looking at them to make sure they aren't bouncing.

 

[Orig69]

Do you have some pictures of the engine?

 

[matchek]

Has there been any change in status if detecting your backfire issue?

 

[Don67Satellite]

as well a 5/16 clear fuel filter

If that's one of those clear chrome/glass ones, throw it in the garbage. They always leak.

 

[cosgig]

Check the spark plugs for a broken porcelain insulator. I’ve had this happen, popping through the exhaust. Replaced the timing chain, plug wires, gapped the plugs, went through the ignition and distributor, a lot of head scratching. Never checked to see if it had a broken plug, which it did. $3 later, no more pop.

 

[Griff]

Good afternoon all,

I'd really like to thank everyone for sharing their comments and ideas. It truly is a fun forum when we can share thoughts and try and problem solve for mopar hobbists, Cheers!

Looks like we may have solved the problem...

 

[Griff]

Run the 12 amp and I'd do it first before you bother tearing anything else apart!

Dadsbee may have nailed it...thanks!

 

[1967coronet]

So....
Seen you just posted, good deal.

 

[dadsbee]

Dadsbee may have nailed it...thanks!

Thanks! I'm here all week!!! LOL... Gone next week....

 

[Griff]

So, this afternoon, I popped a cold one, welcomed the sunshine and opened the garage. Still only 50 here in metro Detroit, but it was nice in the non-heated garage.

I did would Dadsbee suggested. (I did go out and get a vacuum gage like a few others suggested, horrible freight had one on sale for $12.

I charged the battery for about one beer I also left the charger on at 12amps...Turned it over and did my usual warming it up. (Currently, I don't have the manual chock cable yet.) Got it to where it was warm and let it idle. It really runs great...

Almost 15 min., and no bang at all. Well, that meant a 2nd beer and some sun in a chair. Let it sit for about 30 min...left charger on the whole time. Started a 2nd time and ran for about 15 min. and again nothing. Long story shorter, did this throughout the day, a couple more beers and all seems grand in my mopar land!

Maybe Dadsbe or someone else can elaborate on why this seems to have fixed the problem.

As well, is getting the period correct 30amp stock alternator worth getting rebuilt or do I need to bump up to a 60amp or 100amp. I hope this thread can help another person, like it has seemed to have helped me.

Looking forward to reading everyone's comments and banter, Cheers! I will post a few pics I took today.

 

[Griff]

Here are some photos I took today. Oil pressure was at 15min of running, it stays rock steady at 30 went hot and 35 at start up.

 

[Griff]

Other notables...battery charger at 12 amps with car at idle had reading on my cheapo gage, @ 14.43 pretty steady. Without the charger on like I was running yesterday with it still exhaust banging, the gage was reading @12.53 pretty steady.

Also, vacuum gage did not bounce around. I left it on the car the whole day, and the reading moved a few ticks back and forth, but stayed in the green, pretty much where the pic shows it at.

 

[Orig69]

Are you in the process of installing a PCV valve.

 

[Griff]

Are you in the process of installing a PCV valve.

Ya, I need to get one as well and the rubber grommet also. Suggestions on specifics ones with best prices, and purchase places I'm interested in.

 

[Orig69]

I believe Mancini Racing still sells them.

 

[Griff]

cool, thanks...ya that was going to be next weekends purchase with a few other bobbles.

 

[cosgig]

I guess I would suggest to get the 60a alternator, which is at the top of the wirings capability if you’re wiring is still the stock pieces. I am also wondering if you’re still running the single field alternator and mechanical voltage regulator. My guess on why this may have fixed the problem would lie in the fact that low voltage will cause inconsistent voltage throughout the system. That causes electrical components to do all kinds of crazy things.

Yes, a trip to Mancini is always a fun run to make. I forgot you are a Detroit local, as am I. I’d like to see that car up and running in top shape, and coming to a cruise near me!

 

[Griff]

I guess I would suggest to get the 60a alternator, which is at the top of the wirings capability if you’re wiring is still the stock pieces. I am also wondering if you’re still running the single field alternator and mechanical voltage regulator. My guess on why this may have fixed the problem would lie in the fact that low voltage will cause inconsistent voltage throughout the system. That causes electrical components to do all kinds of crazy things.

Yes, a trip to Mancini is always a fun run to make. I forgot you are a Detroit local, as am I. I’d like to see that car up and running in top shape, and coming to a cruise near me!

Thanks Cosgig Yes, single field alternator, but not the old mechanical voltage regulator. The newer style voltage regulator you can see in the pics on the firewall.

 

[Don Frelier]

Looks like you did a nice job putting it together.
Once you get the charging system working correctly you need to drive it.
Long periods of idling isn't a good thing.
A varying load and RPM between 1,500 and 2,500 rpm for a while.
I start with small circles from home and then make wider circles until I've got some run time after major surgery.
Keep checking for any leaks.
And run around and check hoses, carb base and valve covers for loose bolts after a few heat cycles.

I would suggest looking into a steel line from the pump to the carb.
They aren't real expensive and it's pretty easy to find.

Glad @dadsbee was here to help.
Like my Uncle the mechanic used to say "think simple", I miss him.

 

[Griff]

Thank you for the kind words of wisdom Don. Once it warms up outside, i'll be doing just that. I've always done the small circles playbook as you said, until the car and I both feel comfortable, lol.

I've thought about the steel line from pump to carb, but after many discussions, decided to go with the 5/16 Gates fuel line. I may change in the future, if/when I need to change pumps. Right now this brand new one has the 2 nipples, not the fitting on the one end. Also, Mancini had not had the line in stock recently...probably upgrade in the future.