Dying Dart after being warmed up.

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wally_x

wally_x

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Hello awesome /6'ers!

My 71 dart is coming back from the paint/body shop on monday and can't wait to show you guys pictures! In the mean time I was hoping you could help point me in the right direction with the only mechanical problem the old girl is having right now.

First off its a bone stock 225. Right now she starts right up and idles great from sitting over night. Driving from there seems fine, idle seems ok to me and seems to accelerate as well as a 40 year old /6 should. But intermittently (I would say 75% of the time I drive it) after about 15-20 of driving she'll start to sputter out and die when left to idle. Like I'm cruising and it seems to run fine, but once I get to a stop light it dies. To start it again I have to turn the key and keep the RPM's up while in neutral. I'll take off it stays alive at cruising speeds, then dies again once the RPM's get to idle. There have been time where I had to drive it like this for 15 minutes or so to get back home and sometimes the problem seems to fix itself the it can stops dying.

My first instinct is that the symptoms must be associated with heat, but the fact that it sometimes goes away (without getting any cooler) confuses me.

Any advice on where I should start the diagnosis? Retune the carbs idle adjustors? Vacuum tests? I've only had the car for a month or so, and am still learning a lot. Any advice would be awesome gents!
 
Check for vacuum leaks, adjust your air/fuel and idle settings first. It could just be idling a touch too low in gear.
 
carb. coil or points would be where i would start and vacume leaks and maybe the valves my be a little tight when warm maybe good luck
 
My first thought was coil, but a carb/vacuum issue can't be ruled out at this point.
 
after about 15-20 of driving she'll start to sputter out and die when left to idle. Like I'm cruising and it seems to run fine, but once I get to a stop light it dies. To start it again I have to turn the key and keep the RPM's up while in neutral. I'll take off it stays alive at cruising speeds, then dies again once the RPM's get to idle.
Click to expand...
This is what makes me think idle, air/fuel or vacuum leak.
 
I'm thinking vacuum leak, or low vacuum because I also recently add a power brake booster and it feels like it takes awhile for the booster to "charge up". Like at cruising speeds that first tap on the brakes stops like a dream, but at idle or if a pump it a bunch rapidly it looses the "powerness" of it.

Random, stupid question...whats the best way to cap off unused vacuum lines? Also anyone know the best spot I should be tapping into for my brake boosters vacuum line?
YOU GUYS ROCK!
 
dont overlook that it may be flooding out or that its losing fuel pressure. i still have a number of 40+ year old coils that are fine.
 
Also the previous owner added after market MDS electronic ignition for whatever that is worth.
 
The 71 service manual is a free download here somewhere. From that you can determine does your car has ported vacuum switches and other emissions features that can cause problems after the engine warms up. Onlt place to attach a booster is the main manifold vacuum port. It can be any type from a single port to a ( easily broken ) tree of ports on 1 fitting.
Again the factory service manual contains most of the answers you need.
 
I've used golf tees to plug vacuum lines. If I'm not planning to re-use the line I've used screws with a dollop of RTV sealant. When all else fails, try the HELP! section at a well stocked big box part store and look for vacuum caps.
 
When it shakes and dies at idle, especially when shifting from P or N to D or R, it is usually from running too lean. A vacuum leak can cause that since it becomes much more significant at idle. In my case, over 17 years, the problem was the Holley 1920 carburetor. After the ~4th one, it idled perfectly smooth and no more stumbling off the line.
 
Thanks everyone! As soon as I get it back from the body shop on Monday I'll start checking these things!
 
Mines doing the same thing! Mine had a bad hesitation when pulling out, and after adjusting the valves today, mine seem to get worse. But when I looked down the throat of the carb at idle, it is spitting fuel. Like "sputtering noise". Holley 1920!
Hopefully my valves are right, because it wasn't as bad before. But my carb sat for 15 years with the same fuel in it. ugh!!
 
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