Occasional no start mystery

[Dibbons]

Once in awhile, first thing in the morning, my original '72 318 SSP won't start. The starter spins just fine, but no ignition. I know it has fuel because I first operate the carb accelerator pump by hand to squirt a couple of shots of gasoline into the intake manifold and I can feel/hear the gas squirt. Compression checks out fine and engine purrs like a kitten while idling. Must be ignition.

My first question is this: When the ignition ballast resistors fail, do they fail completely and forever or do they work one minute and don't work the next, and then work again later? Note:The vehicle has a new single point distributor (made in Taiwan, sold by PepBoys). The ballast resistor is two wire type, not four. Thank you.

 

[Glenwood]

once a resistor fails, it's gone.
You may have a bad coil. I suggest checking the point gap & dwell and timing to make sure it's all on spec.

 

[PurpleBeeper]

once a resistor fails, it's gone.
You may have a bad coil. I suggest checking the point gap & dwell and timing to make sure it's all on spec.

This is good advice. Ballast resistors are all or nothing. I had a similar issue with electronic ignition (ignition box), but you say you're running points. You might also check your electrical connections to see if any are loose/corroded. Maybe it's the brown wire that bypasses the ballast resistor or something in the ignition switch???

 

[Dibbons]

As a side note, I just saw a ballast resistor for sale that was listed as "electronic", what's up with that?

 

[Lionized]

This will have nothing to do with your ballast resistor as it is bypassed during ignition. Try another coil if you have one kicking around.

 

[HEMI-ITIS]

Could also be the ignition switch.Check for power at the coil in start & run mode.

 

[bigmanjbmopar]

Here is a good video on testing your coil, Plus an old points system could just have some junk on the points, when is the last time you sanded them clean / adjusted?

https://youtu.be/h8vSwfnX3Xc

 

[Glenwood]

that's a good video. Keep in mind that the coil resistance changes with temperature changes. The colder it is, the higher the resistance, the lower the voltage. Looking at the op's location, I doubt that cold temperatures are an issue but if your coil is on the edge of the spec, a cool evening or morning can cause trouble. Happened to my ram truck.

 

[mopar 3 B]

Or a loose distributor condenser wire shorting to the housing. If this happens all ignition current goes to ground.

 

[Dibbons]

Idle speed is 700 rpm, dwell checks out at 23, should be 30-34, I'll have to work on that tomorrow.