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1981 datsun 310 starts and runs but then will stop

i recently bought a 1981 datsun 310. it has run relatively well but recently when it has been below zero it has had isssues starting. on 3 different occasions i have started the car and had it running, even revving the engine and then the engine will just stop. when i try to start it the car will turn over but will not start.

if i come back later that day or the next it will start right away. one time, when i pulled it in a neighbors garage and warmed the car with a torpedo heater, it started within 10 minutes.

i am wondering if this sounds like a frozen fuel line or filter. i have run 3 bottles of iso heet through the engine in the last 3 fill-ups and it helped a little to make the car run better in the cold. but when i first started using the isoheet i wasn’t having problems starting it.

it’s just the cold and i know i probably need a circulating block heater to solve the problem but i was just making sure it is not something else.

thanks for any help with my question.

How about new plugs, distributor cap, rotor and plug wires? You know, a basic tune up plus checking ignition timing.

Could be carburetor icing, I suppose. Next time it happens, take the air cleaner off and see if you have ice building up in the air horn. This is a relatively uncommon problem on cars, but it does happen occasionally (on old carbureted vehicles like yours) and matches your symptoms. Most of the other likely explanations are fuel supply problems. If you don’t have carb ice, then next step would be to have somebody pump the gas pedal once or twice while you look down the carb throat; you should see a jet of gas from the accelerator pump (if you don’t, then fuel probably isn’t getting to/through the carb).

It also sounds like a bad igniter, if they had them back then. The vacuum advance could be leaking or stuck in position. And whatever anybody else has posted or will post. The hose may be missing from the choke stove.

The next time it happens, remove the coil wire from the center of the distributor, hold it near (1/4") any metal and have someone crank the engine. If there is spark, that’s not the problem. Concentrate your efforts on fuel delivery. 1981 was THE WORST year for engine controls. It was the First Year cars had engine control computers. Crude stuff, quickly abandoned by the manufacturers. The “feedback” carburetors could be expensive nightmares to repair or replace. Some car makers were able to postpone this and get emissions extensions. Hopefully your Datsun is one of those…

If you find you have no spark from the coil, replace the electronic ignition module if you can find one…

I doubt the problem is moisture in the fuel system after 3 bottles of Heet.
Agreed that you need to determine if a spark is missing during this or if it’s a lack of fuel as a first step.

Also curious about the affect of your foot on the accelerator pedal, etc.
Will it die anyway even if the pedal is depressed quite a bit?
When it dies, does it die instantly or does it cough and sputter a bit first?
When it does start right up does it run rough for a bit before clearing up?