Shuts off when hot?

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pink340swinger

pink340swinger

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I have a recently restored 1970 340 4-speed dart. Factory dual point ignition. Everything is either NOS, new or restored. When I start it up it runs until it warms up then stalls and won't restart until it cools off. All voltages seem to check out, both before starting and after it stalls both to the ballast and to the coil. Carb is good, fuel is getting to carb ok, seems like some sort of heat sink but I can't find it. It's just me so I'm not able to check under the hood and under the dash at the same time for wiring issues. Harness is new, bulkhead connectors have been checked and rechecked several times, same with fuse box. Alternator has been restored, two new coils have been swapped in and out, with the same results. NOS ignition switch, good original turn signal switch, distributor was rebuilt and setup on a machine for dwell and advance. I'm not interested in changing to electronic ignition so please don't waste your time posting any replies stating that. This is a restored, stock appearing car. It turns over fine after it stalls but doesn't really even try to fire, carb shoots fuel when I pump it just fine so I'm sure it's not a fuel issue. I've cleaned up grounds in several places. Any ideas?
 
Does this just happen idling in the shop, or out on the road too? When it dies, does it seem like it's getting rich? Maybe a high float setting, or since it's all stock, a stuck heat riser on the pass manifold.

Just reaching for straws since you have almost everything else covered.
 
choke not opening?
Choke should pull off a little bit immediately upon starting.
Then open further based on temperature of the choke's bimetal coil.
 
No choke on it, not flooding. Haven't made it out of the shop, brand new build, won't stay running long enough to get out of the shop...
 
I tried 2 different professionally restored AVS carbs with the same results so I put my known to be good 750 Holley on it. Runs smoother and better than the other carbs as I wasn't able to get them adjusted to my liking. Idles well, takes fuel and revs well, but just dies after it gets warmed up, 5-6 minutes or so..
 
Not many things with points set up that will fail just because they got a little warm.
Maybe the condenser.

If there's no choke, and it starts easily, could be too rich when it warms up. Normally (in my experience) too rich will die when load is put on it, not in neutral.
 
It's definitely not a carb/fuel issue. When it does start to die I've tried giving it gas but it stalls anyways. Doesn't matter if its at idle or I'm reving it or at a high idle, once it starts to die there's nothing i can do to keep it running.
 
Not sure if a points system using a ballast resistor or not, but I had a duster that when the ballast resistor got hot it would drop voltage
 
Could be a bad capacitor (condenser) in the distributor. I do not use automotive/ OEM style caps in my outboard motors. I use plastic "electronics" plastic film. Sprague "orange drop" are good ones.


Try to "get ready" to test as soon as it quits. Get a WIRE core wire to test with for the coil secondary, and make or buy a spark test gap. As soon as it quits, leave the key in "run" don't disturb it. Get a test light or meter on the coil+ and see if you have "run" voltage there. It will not be full battery voltage, should be (varies) 5-10V or so

Next "rig" your spark test gap, and crank the engine USING THE KEY. Watch the test gap and see if you have spark.

If not, put a test lamp on the coil NEG and bump the engine (such as jumpering the start relay) until you have a light or voltage. This shows the points are opening. Bump till they close. Check voltage both coil NEG and coil POS. Again, with key in "run," coil + should be about 5--10V or so. Coil NEG should be quite low, probably not more than 1V

So far as the cap (condenser) ignore all the www. BS about testing caps. There is only ONE WAY to test a cap and that is with a HIGH VOLTAGE leakage tester, because if it is "weak" and leaky, you want it to break down if it is going to. Over a hundred volts. After leak checking THEN you can check for proper capacitance value.

(I'll have to look that up, don't remember off hand)

You obviously could just replace the cap, but no guarantee that the new one will be better
 
When it fails to start, remove a plug lead & lay the lead on the valve cover, screwdriver inside; create a 3/16" to 1/4" air gap. Crank & watch for white/blue spark. No spark: obvious; yellow spark = weak spark.
 
Bewy said:
When it fails to start, remove a plug lead & lay the lead on the valve cover, screwdriver inside; create a 3/16" to 1/4" air gap. Crank & watch for white/blue spark. No spark: obvious; yellow spark = weak spark.
Click to expand...
Bingo. If I had to guess, it loses spark. May not even be "heat" related, but masking itself as so. I chased an ignition gremlin from engine to engine once from a bad distributor pickup. I have never messed with points, but I still lean on the distributor losing spark on This one.
 
I bet it is the Capacitor. Even NORS and NOS can fail. Especially when they get hot. Should test usually .25-.285 MFDS
 
Thank you everyone for the suggestions, the issue has been with 3 different distributors, a single point, a pertronic electric, the factory dual point both before and after being rebuilt with NOS parts and run on a SUN machine to test it. 2 new coils and one known good used coil taken off my other car. I've checked voltages at the coil, ballast, junction block, ignition switch connector, with all different configuration of carbs, ballast, distributors and coils that I can't remember all the results other than it dies after it warms up. I will try more diagnostics today.
 
Right when it dies check the voltages starting at the ballast resistor to the rest. Hard to find a issue if it "cools" off and runs. Prob something simple. Like a dirty connection somewhere.
 
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