Need some ideas

[Sheriff41]

Just to rule out a restricted muffler, you could do the rev engine and hand test the exhaust pipe outflow, to see if there is a noticeable difference. It’s a long shot, but something else to check off the list.

Seems to flow fine for the few minutes it runs. Has the sound I was looking for, too! Thanks for the idea.

 

[Sheriff41]

If you have any electronics like ignition modules on the car you have to disconnect them. At least the ground wire but I disconnect both. Disconnecting the battery won't protect them when welding. Sometimes welding can partially damage a module and cause the symptoms you have. If you still had the exhaust pipes connected to the engine you could be putting weld voltage throughout the chassis. Just a stab in the dark.
After reading your post again I see you use points. Perhaps the condenser has gone kaput?
A real head scratcher for sure. Interested in what you find, hopefully sooner than later!

Well, I did not have a spare condenser (have to correct that) and hardly any parts stores stock points and condensers, let alone for a factory dual point dizzy. Waiting on parts delivery...

 

[Cleveland Crush]

Yeah, I didn't think the mufflers would make that much difference but figured I should ask.
There is fuel in the bowls. It's a Holley 4160 750cfm I've been running for a few years. Easy to check the fuel level in the bowls. It does have an electric choke - could welding the pipes caused a problem with the choke? I checked the choke and it seems to be functioning properly.

When it stalls out, prop the choke open and see if it then starts. If still no start, quickly rig up a spark checker to verify plugs are firing.

 

[basstrix]

Yeah, I didn't think the mufflers would make that much difference but figured I should ask.
There is fuel in the bowls. It's a Holley 4160 750cfm I've been running for a few years. Easy to check the fuel level in the bowls. It does have an electric choke - could welding the pipes caused a problem with the choke? I checked the choke and it seems to be functioning properly.

I suppose it's possible something happened to the choke circuit related to the welding. I've heard of voltage spikes taking components out....and RF if you're TIG welding with a high frequency stabilizer.

Since it has fuel, I think it's choke related. I think someone has already made a good suggestion to prop open the choke and try it after it dies.

 

[Don C]

Have you changed the condenser, yet? If not I would change it, and I would also get a spark checker and see if you're getting a spark after it dies.
https://www.harborfreight.com/search?q=spark plug tester
The coil is another possibility.

 

[Sheriff41]

Have you changed the condenser, yet? If not I would change it, and I would also get a spark checker and see if you're getting a spark after it dies.
https://www.harborfreight.com/search?q=spark plug tester
The coil is another possibility.

Thanks Don. I will pick up the condenser tomorrow from NAPA and give it a shot. A spark tester is probably a better idea than the old screwdriver-and-a-ground method I usually use. @Cleveland Crush suggested the same.

 

[AcesArneson]

Was the battery connected when you were welding? When you have it started check your voltage to see if you are getting charging voltage. Might have fried the alternator when welding.
When it dies does it just quit or does it sputter a bit?

 

[Sheriff41]

Was the battery connected when you were welding? When you have it started check your voltage to see if you are getting charging voltage. Might have fried the alternator when welding.
When it dies does it just quit or does it sputter a bit?

Battery cables were disconnected. Didn't think to look at the amp meter so I'll add that to the list - thanks!
Runs like normal for a couple minutes then the RPMs just drop until the engine quits running. Attempts to restart will crank, fire, and quit. Let it set for 30 minutes and it goes through the same sequence. I'll have more info tomorrow after I have time to try the ideas everyone has suggested here.

 

[71coop]

Maybe a dumb question, but is the choke coming off/operating correctly as it warms up?

 

[70cobrascj]

Nope, all well clear. They're Precision Exhaust items and made on a jig for 71-73 Mustangs with staggered rear shocks. They fit very nicely.

Pic of the tail pipes?
Is it possible any packing material could of been in one of or both pipes and plugged the system up?

 

[70cobrascj]

Maybe disconnect the exhaust at the headers and see how it runs

 

[Sheriff41]

Maybe a dumb question, but is the choke coming off/operating correctly as it warms up?

Yes, it appears to be working.

Pic of the tail pipes?
Is it possible any packing material could of been in one of or both pipes and plugged the system up?

No, good flow through the exhaust.

 

[cjstaci]

It was running fine before the exhaust work, could the mufflers be so restricted to cause it to die, seems doubtful, but I suppose anything is possible.
I would start it and when it starts to die, goose the throttle a couple times and look to see if it’s getting a good squirt of fuel. If it’s getting the fuel and still dies, then check for spark. Could be a coincidence that the condenser or coil has failed. If you have good spark and fuel, then do what 70cobrascj said, uncap the exhaust at the headers, that will either identify or eliminate the exhaust system as being the problem.
I love these old cars, but sometimes they like to see you struggle a bit before you get to enjoy them, lol

 

[Sheriff41]

Well, like I said, this car has purposely caused me problems in the past. I got home from work, armed with condenser, coil, spark plug tester, and prepared to loosen the exhaust from the headers. Decided to give it one more try... and it fired up! The choke did its thing and the engine revved until it began to warm up. Blipped the throttle and it settled down but seemed to be a little rich, so out with the vacuum gauge, some fine tuning on the idle mixture and she seems to be happy. Idle set screw is just off fully closed so the transfer slots are not too exposed. Hmm. Finicky old car! Maybe it was upset with me for going to Japan for a week after installing the new mufflers. I swear these cars have minds of their own!

I don't have time to drive it this evening but I let it run for a good 30 minutes or more. I'll take it out for a drive after work tomorrow and follow up with you all if anything changes.

Anyway, thanks for all the help and ideas. Gotta love this site!

 

[Cleveland Crush]

Well, like I said, this car has purposely caused me problems in the past. I got home from work, armed with condenser, coil, spark plug tester, and prepared to loosen the exhaust from the headers. Decided to give it one more try... and it fired up! The choke did its thing and the engine revved until it began to warm up. Blipped the throttle and it settled down but seemed to be a little rich, so out with the vacuum gauge, some fine tuning on the idle mixture and she seems to be happy. Idle set screw is just off fully closed so the transfer slots are not too exposed. Hmm. Finicky old car! Maybe it was upset with me for going to Japan for a week after installing the new mufflers. I swear these cars have minds of their own!

I don't have time to drive it this evening but I let it run for a good 30 minutes or more. I'll take it out for a drive after work tomorrow and follow up with you all if anything changes.

Anyway, thanks for all the help and ideas. Gotta love this site!

Perhaps your Stang got scared and decided to start running right, after hearing all the things we suggested you do to it..!!

 

[Steve McMahan]

“I know what happened. You jacked me up and installed the new exhaust system. That lifting caused something in the fuel tank to partially clog the fuel inlet. It’s still in there and I’m not sure it won’t cause the same problem.”

Signed, Your Car

 

[Sheriff41]

“I know what happened. You jacked me up and installed the new exhaust system. That lifting caused something in the fuel tank to partially clog the fuel inlet. It’s still in there and I’m not sure it won’t cause the same problem.”

Signed, Your Car

Lol! You may be right. I do have a new fuel tank, pickup, and sending unit on deck, thanks to another member of our group. Project for another day.

 

[Roland]

It was running fine before the exhaust work, could the mufflers be so restricted to cause it to die, seems doubtful, but I suppose anything is possible.
I would start it and when it starts to die, goose the throttle a couple times and look to see if it’s getting a good squirt of fuel. If it’s getting the fuel and still dies, then check for spark. Could be a coincidence that the condenser or coil has failed. If you have good spark and fuel, then do what 70cobrascj said, uncap the exhaust at the headers, that will either identify or eliminate the exhaust system as being the problem.
I love these old cars, but sometimes they like to see you struggle a bit before you get to enjoy them, lol

I assume you checked the IN and OUT flow direction on those new mufflers?

 

[AcesArneson]

Well, like I said, this car has purposely caused me problems in the past. I got home from work, armed with condenser, coil, spark plug tester, and prepared to loosen the exhaust from the headers. Decided to give it one more try... and it fired up! The choke did its thing and the engine revved until it began to warm up. Blipped the throttle and it settled down but seemed to be a little rich, so out with the vacuum gauge, some fine tuning on the idle mixture and she seems to be happy. Idle set screw is just off fully closed so the transfer slots are not too exposed. Hmm. Finicky old car! Maybe it was upset with me for going to Japan for a week after installing the new mufflers. I swear these cars have minds of their own!

I don't have time to drive it this evening but I let it run for a good 30 minutes or more. I'll take it out for a drive after work tomorrow and follow up with you all if anything changes.

Anyway, thanks for all the help and ideas. Gotta love this site!

Alls well that ends well! Head scratcher.

 

[MAD IRISHMAN]

It was probably a muffler bearing that finally loosened up!