‘71 Dart with 340 motor stalling problem

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BRog

BRog

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Greenwood, IN
Dart keeps stalling after running for 15 or so minutes. I’ve replaced the ecu, coil, ballast resistor, fuel pump and carb. Thinking it might be vapor lock, I even put a heat sleeve on fuel line - still no good. Car runs super strong for first ten to fifteen minutes. After it’s run warm for a few minutes I can feel it begin to stumble when just cruising 30-40 mph. Pedal will cut in and out for a few miles then normally (or maybe coincidentally) when I let off gas to slow down or come to stop engine cuts out completely. Not sure what else to check at this point. Any idea what would cause a stall like this after motor runs at temp for awhile? I should also mention that the engine temp is good. I have an electric fan that keeps coolant temp around 180-185. Could it be a wiring/grounding issue that shows up when engine bay gets warm? Getting a little frustrated because it runs so good when cold. Any thought would be greatly appreciated.
 
Sounds like fuel issue. Might be possible there is junk in the tank that clog the pickup filter. Then when suction is lost the debris falls away. Good luck.
 
Have you checked to see if you have fuel in float bowls when this occurs? What does your fuel system consist of? Have you loosened fuel cap when this occurs? Could be wrong fuel cap or a vent system plugged. If it does stall and you loosen cap and hear it pulling in air that could point to vent system. If you have factory exhaust manifolds do you still have the butterfly installed on passenger side. Maybe it’s stuck partially of fully closed. Does it have a choke and is it operating correctly. Just some things I’d check personally.
 
I agree its in the tank they run good until it stopped up and when you shut them down the trash falls off the filter ,sometimes it takes hours for it all to come off.
 
Have you verified the reluctor gap in the electronic ignition distributor????
 
BRog said:
Dart keeps stalling after running for 15 or so minutes. I’ve replaced the ecu, coil, ballast resistor, fuel pump and carb. Thinking it might be vapor lock, I even put a heat sleeve on fuel line - still no good. Car runs super strong for first ten to fifteen minutes. After it’s run warm for a few minutes I can feel it begin to stumble when just cruising 30-40 mph. Pedal will cut in and out for a few miles then normally (or maybe coincidentally) when I let off gas to slow down or come to stop engine cuts out completely. Not sure what else to check at this point. Any idea what would cause a stall like this after motor runs at temp for awhile? I should also mention that the engine temp is good. I have an electric fan that keeps coolant temp around 180-185. Could it be a wiring/grounding issue that shows up when engine bay gets warm? Getting a little frustrated because it runs so good when cold. Any thought would be greatly appreciated.
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krazykuda said:
Have you verified the reluctor gap in the electronic ignition distributor????
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will check all of the above, thanks guys
 
Is this a hydraulic lifter engine?

Then I would check the plugs,when she stalls, I bet they are overheating, indicating a very lean cruise AFR.
But
During the warm-up period,you say she runs super strong, so not lean at that time.
So then, have you tried removing the gas cap at the time of the stall checking for vacuum there.

It really sounds like too-tight valve lash when hot.This can happen with hydros too, with too-long pushrods.
 
What fuel are you running? Pump gas with ethanol?
 
Sounds like you have a common 71 fuel vent problem. Drive it with the cap off . Make sure the vent line coming to the engine compartment on the passenger side is open. 71's have a none vented cap and a sealed vent system that ends on the breather cap on the passenger valve cover. I have seen these lines plugged. and or crimped shut. Or rotted through at the vent tube and clogged with rust.
 
Oldmanmopar said:
Sounds like you have a common 71 fuel vent problem. Drive it with the cap off . Make sure the vent line coming to the engine compartment on the passenger side is open. 71's have a none vented cap and a sealed vent system that ends on the breather cap on the passenger valve cover. I have seen these lines plugged. and or crimped shut. Or rotted through at the vent tube and clogged with rust.
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Oldmanmopar,

This was originally a slant 6 car that I did a motor swap on. When I did the swap, I removed the little black can that sat on passenger side of engine compartment. I assumed the 1/4” line that came off tank to the can was a vapor return line and not a vent line, so I put a cap on it. Is it a vent line? Should I leave it uncapped? I’ve researched the gas cap I have and it is definitely not original to a ‘71. Someone has replaced the original with a ‘72-‘73 cap and obviously replaced filler neck as well. Assuming I probably do have a venting issue, but not sure how I should be set up to correct it. Tank has one barb that sits above sending unit which is connected to 1/4” line I referred to earlier (which I capped up in engine compartment). I don’t see any other way that I’m venting unless that ‘73-‘74 gas cap is vented.
 
did you drive it with the cap off? Do not assume this is your problem unless you check if it goes away with driving it with no cap. Then lets go from there.
 
BRog said:
Not yet. Will do and let you know. Thanks
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Posting from side of road. Totally stalled again. Gas cap off doesn’t cure it. Same as always, went for 10 minute drive. Stopped at hardware store for 10 minutes, fired it up and it stalled on my way out of the store parking lot. I was able to pump pedal and get it to fire up but would only run as long as I keep one foot on break so I can keep rpms up. As soon as I let off gas it stalls again. Vapor lock or something else?
 
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