Baby it's cold outside.

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Michael Hurst

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Ok, it's chilly out, and when i've taken my all stock 1970 Valiant out the past couple of times when the temperature was below 50 once the car warms up it wont idle.
When the weather is warmer the car starts and idles just fine. Just seems to be an issue when the car is warm but the air is cold.

Any thoughts?
 
My thoughts, fill the gas tank up with some fresh gas and drive it to Baltimore and back...lets us know how it idles then.
 
Your carb is icing up, it dose not have to be freezing out for this to happen, it simply happens when the volume of air rushing through the venturi of the carb ( like an hour glass ) rapidly cools the air and ice crystals form inside the carb, sometimes it actually looks like a little snowball in there, if you lift the lid from your air cleaner while running you may see it, it was always a common problem on many cars including Chrysler products through the eighties even, you simply need to make sure the warm air from the exhaust manifold reaches the carb through the bottom of the air cleaner snorkel, if all is set up right once the choke is off the engine should start to be warming up and as the manifold gets hot there may be a thermostatically operated door in the bottom of your air cleaner snorkel that will open and close to allow warm air in however on a 70 I am not sure if that was out yet may be too early if so it is not difficult to fashion a stove pipe ( cardboard style heat proof tube you could purchase at Napa or ) to go from the manifold to air cleaner bottom, that should keep the carb from icing, google it you will see what I mean.
 
Also, a working heat riser directly under the carb is very important too.
My 64 is cold blooded but a short time after starting runs very well. The time depends on outside temp.
 
Thanks to everyone for your suggestions, I believe that I've found the issue.

Only one part was missing. The vacuum hose from the snorkel valve to the underside port of the thermal switch was missing.

After adding the hose, and firing her up, the snorkel valve was completely closeed and pulling air off the manifold. After she was warm the valve was shut and she ran like a top in ~40deg air.

Thanks again.
 
Glad you figured it out. My slant runs well even when the temp gets to -10f here in MN.
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Your carb is icing up, it dose not have to be freezing out for this to happen, it simply happens when the volume of air rushing through the venturi of the carb ( like an hour glass ) rapidly cools the air and ice crystals form inside the carb, sometimes it actually looks like a little snowball in there, if you lift the lid from your air cleaner while running you may see it, it was always a common problem on many cars including Chrysler products through the eighties even, you simply need to make sure the warm air from the exhaust manifold reaches the carb through the bottom of the air cleaner snorkel, if all is set up right once the choke is off the engine should start to be warming up and as the manifold gets hot there may be a thermostatically operated door in the bottom of your air cleaner snorkel that will open and close to allow warm air in however on a 70 I am not sure if that was out yet may be too early if so it is not difficult to fashion a stove pipe ( cardboard style heat proof tube you could purchase at Napa or ) to go from the manifold to air cleaner bottom, that should keep the carb from icing, google it you will see what I mean.
What an excellent post!
You took the words right out of my mouth...........
 
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