Backfire thru exhaust at idle

[eldubb440]

coil heating up?

 

[Griff]

Alternator is stock date coded 1968, it reads 12.53 on my cheap hand probe at battery when running.

 

[WileE]

A vacuum gauge is a mandatory tool in any mechanics toolbox. Rather than another thread with arrows shooting all around to find a target, do this. Hook up a vacuum gauge, take a reading. You'll probably then should do a compression test ( another mandatory tool, you do have one ? ). There's a number of things that could cause your symptom. Fuel and electrical don't mean squat unless your mechanicals are functioning properly.

 

[eldubb440]

Ran again today, runs super strong, lightning quick throttle response and again about the 13 min. mark started to bang again, not quite as load or strong a few times at idle. Crack throttle open and it roars and no bang.

it does it after about 13 minutes? it did this more than once?.......sounds electrical to me

 

[Griff]

Fuel pressure could be hot, it is a brand new fuel pump stock, not round race pump. I had originally ran fuel line up over passenger fender well, and had mounted clear fuel filter there. The original fuel line, ( still in car) was bent upwards, so I just ran it up over wheel well and over to carb.
FYI- this build is not going together totally stock and/or year correct. I have put battery in trunk, running a 72-440 with 70' stock 440 intake. Cam is Crane .488 int / .491 exh - @.050 - 230 int. / .236 exh. lobe 110

 

[Griff]

You are correct WileERobby, my bad, they will be in my tool box this week

 

[Griff]

Yes,

it does it after about 13 minutes? it did this more than once?.......sounds electrical to me

After I clean all the plugs, it waits till warm and about 13min in to the start up

 

[Griff]

coil heating up?

Coil is a stock unit, new like most components, does not seem overly warm

 

[dadsbee]

I gotta ask... are you charging the battery back up between these runs??? 12.53 volts certainly doesn't impress me. A static battery, fully charged, should read more than that!

 

[440 PHIXX]

The dopey kidz today “tune” their junk to do that.

 

[70bigblockdodge]

Misfiring and raw gas is burning/ popping in the hot exhaust. You have a misfire, bad plugs or bad wires, 13 minutes is the time it takes to get the exhaust tubing hot.

 

[Griff]

When I mean, fuel pressure was running hot...after I made change of running fuel line now straight under headers, then up through front of block to hard fuel line off carb, I had not realized it was a 5/16 line as well a 5/16 clear fuel filter. Fuel sprayed at high pressure from rubber hose connections. switched to 5/16 line from pump to carb and fixed problem. Still have 3/8 rubber line from steel fuel line (original) to pump. Initially the fuel did not spray when I had clear filter mounted on inner fender, and I think that was causing a slight vacuum leak at filter and not creating the high pressure to carb (I had 3/8 line on both ends at that time). Also, rear end was up in the air, so I thought I was causing a lean cylinder or 2. But, all plugs (when pulled were wet)

 

[Griff]

Misfiring and raw gas is burning/ popping in the hot exhaust. You have a misfire, bad plugs or bad wires, 13 minutes is the time it takes to get the exhaust tubing hot.

That might be the ticket, with my 2" headers some of the wires are right up on the exhaust. I saw that early on an I am running each with high quality plug "socks"

 

[Griff]

I gotta ask... are you charging the battery back up between these runs??? 12.53 volts certainly doesn't impress me. A static battery, fully charged, should read more than that!

Yes, I have been charging battery up between runs and it reads about 13.67 before starting

 

[Griff]

I really do appreciate all the comments guys, it's nice to chat in cool forum like this. It's been a long time for me

 

[dadsbee]

Yes, I have been charging battery up between runs and it reads about 13.67 before starting

So your alternator is doing squat and 13 minutes in your ignition system goes into clusterfuck mode from low voltage. Leave the charger on the battery and run her up again !

 

[Griff]

So, as WileRobby stated, I'll be doing: compression test / vacuum test tomorrow. What numbers should I be looking for? And fairly novice on some aspects here, where would I pull vacuum from and at what RPM?

 

[Fran Blacker]

A long shot. Do you have a Carter mechanical fuel pump on there. Carter M6903 High pressure pump. Edited.

 

[Griff]

So your alternator is doing squat and 13 minutes in your ignition system goes into clusterfuck mode from low voltage.

That came up as well in my thoughts, but I believe the alternator is the stock 30 amp 1968 / and when tested at O'Riellys they tell me it "passed"

 

[Griff]

A long shot. Do you have a Carter mechanical fuel pump on there. I don't know the P/N but it puts out to much pressure. @khryslerkid knows it.

I think it might be, I got from Mancini a bit ago, but it is brand new and just put on for this build. I'll need to check that for sure tomorrow. So you think it's rushing fuel past floats...clear filter is full.