Why does engine cut off after idling for awhile?

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wh23g3g

wh23g3g

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On this 65 Valiant 170 I've got. It starts up easy and idles good. It's got the most vacuum I can get out of it for it's wear and tear. It's between 16-18 in-hg at idle. It appears the motor has some miles on it but it idles smooth and no unusual noises. All electronics have been gone through and many replaced throughout the last 2-3 years and not driven but a few miles. I usually start it up, get temp up, and drive it around the neighborhood a few times since it's not perfectly streetable. Now it's developed a symptom of dying minutes after idling smoothly. I start it and let it fast idle for a minute and then hit the gas and idles around 600-650 real smooth and quiet. I let it get up to normal temp, but sometimes it just cuts off. It has fresh fuel too and it has 5-6psi fuel pressure too. It's still running points which the distributor was changed out with a reman probably 2-3 years ago but probably only been driven 10-15 miles but started and idled on a regular basis. Any ideas? Ballast resistor, maybe?
 
Does it fire back up right after it dies?
 
If it just cuts out,it's usually ignition failure. Put a voltmeter on the coil the next time it happens.If you still have around 6 volts, I would replace the condenser in the dizzy, and retest. While the cap is off check it for moisture,and carbon tracking.If the problem persists,have the coil tested.
But if the voltage is AWOL, check the voltage on the input side of the ballast resistor. If voltage there is near battery voltage,jumper across the resistor and retest. If the problem goes away, replace the resistor.
But if the voltage at the input side of the resistor is awol,check the bulkhead connector.Then the Ammeter-both sides. And finally the ignition switch.
Happy hunting...................lol

Coiltest;This must be done immediately after the engine shuts off.Remove the coilwire from the cap tower and near-ground it,about 1/4 inch. Have a helper crank the engine with the key. A healthy spark means all is ok. No spark means you have an ignition problem; it could be the coil or the dizzy, or the supply voltage, or the ground...That's where the voltage checks come in.
When everything other than the coil tests out good, then it's time to check the coil.
Here's my way;
With the engine off I remove the coil neg. wire . I jumper a wire over to it ,long enough to reach the fender.I lay a long flat bastard file across the engine somewhere, so it is grounded back to the battery. I near-ground the coil tower-wire.I turn on the ignition to run. Finally I lightly drag the bared jumper wire along the file. A stream of sparks should issue from the tower-wire. You need the file to make/break the circuit. I have not been able to reliably cause the spark-stream any other way, besides pulling the dizzy and manually spinning the driveshaft, using a known-to-be-good point-set and condenser;grounding the dizzy.
I have been using the same big square Accell Supercoil,P4120889,since 1999.Seems to work for me.
 
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It doesn't back fire or idle down, it just straight up quits running. Like someone turned it off. I have the Accel coil on there. It's not but maybe a year or two old. It's got a what I still consider a new engine harness even though it's a couple years old from Year One. The wires, cap, rotor, and distributor are all with a year or two old and not but a few miles. I will tell you that the plugs are new and I'm sure it's something to do with it somewhat. But they get fouled out quick with oil. It could definitely probably use some valve stem seals is what my mechanic said when he checked it last summer. I can believe it probably needs a full head rebuild. It smokes lightly when it's first started after awhile of sitting for a few seconds and then goes away. That's why I assumed the engine has some miles on it. It's not even the right engine. Someone swapped a 225 for a 170. It's now got a 66 170 and 44 less horsepower, probably a lot less now. I just was leaning towards an electrical malfunction. So I'll have to do some checking.
 
bypass the ballast resistor for a trip. It wont hurt anything for an hour. The ballast resistor gets hot and changes resistance (more) to reduce voltage to points so they last longer. yours could be cracked/defective and going open.
 
I see AJ already mentioned the condenser. :D
Cheap enough and could very well be the problem.
 
Those stupid little magic cans have tripped me up a time or two. If they are not grounded they don't work. And neither will the engine run. Yet they can run for a million miles when they feel like it,lol.
 
Very common: The coil gets hot and shorts out, especially if mounted horizontally. They are not expensive. I'd get a new one and make sure it is mounted vertically.
 
AJ/FormS said:
Those stupid little magic cans have tripped me up a time or two. If they are not grounded they don't work. And neither will the engine run. Yet they can run for a million miles when they feel like it,lol.
Click to expand...

I had a guy want me to do a tuneup on his Volvo marine engine because his fishing boat died and wouldn't start out at sea.
He had it towed in to the tune of $2,300
He bought all the parts MINUS the condenser and I asked him to get one, but he said they either work or they don't. (I knew better) but he wouldn't listen, so I did the tuneup using the old one.
Next time he took it out the same thing happened about 25 miles out and cost him another $2,300 to get towed in.
He was pretty pissed off at me now, and demanded I go find out what the problem was.
I connected it up to water and let it sit there and run on the trailer and about 1/2 hr later it started missing and sputtering.
I went to my toolbox and grabbed an old condenser I had in there and grounded it to the distributor casing and touched the lead to the coil + wire and it smoothed out and ran fine.

$1.29 part cost him $4,600 because he wouldn't listen to reason and knew better than the mechanic he hired to do the job.
 
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