The Ford Barn

shew01 · 12-11-2020, 07:04 PM

I’m still learning about the Model A ignition system (and tachometers, for that matter), and I’m wondering if a bad tachometer could make a Model A hard to start. Here is some background information.

Around the beginning of November, I noticed that my tachometer (https://www.westach.com/product-page/2ct32-6v), purchased new in May of 2020, was acting flakey from time to time. (From May to October, the tachometer worked fine.) While idling at a stop light, sometimes the needle would “float” high, but there was no corresponding change in the engine sound, and then the needle would eventually drift back to 500-700 RPM or so, again without any change in the engine sound, meaning that the RPM sounded constant, but the tachometer erroneously indicated a change in RPM. Also, while driving at what was likely to be 1500 to 1800 RPM, the needle would sometimes waft up to 2200 to 2500 RPM, with no perceptible change in the engine sound. Apparently, the tachometer sometimes has a mind of its own and displays whatever it wants to display. The unit appears to be under warranty; so, I need to call about it.

However, I’m curious. For the last couple of weeks, the car has been uncharacteristically hard to start. (https://www.fordbarn.com/forum/showthread.php?t=289945) I’ve jumpered the junction box posts together to take the ammeter out of the equation as a potential problem. I’ve tried a number of different coils (two oil filled coils and one Ford script coil) and two condensers. I’ve thought I had the problem solved a number of times, but the car would continually “backslide” into hard starting over the course of a couple of days.

I have observed the following while working through this issue.

I‘ve used a Sparklite (https://www.brattons.com/ignition-sp...il-tester.html) a number of times when cranking the engine, and I’ve noticed that the engine does not “catch” unless there is a fairly bright LED flash at some point from the Sparklite. (A weak spark sends no flash to the LED or just a faint flash to the LED.)
When the car did “catch,” I would always see a strong LED flash from the Sparklite as the engine "caught," and a strong LED flash would continue while the engine was running.
The engine is hard to start with or without the Sparklite connected. So, the Sparklite does not seem to be causing any of the problem.
Not considering that the tachometer could be a potential problem (until now), I’ve always connected the tachometer to both terminals of whatever coil I’ve had in place.
Regardless of the coils and condensers, the car would still be hard to start at some point, regardless of whether the engine was hot or cold.
I’ve checked the points a number of times, and they are set at .018.
The distributor shaft does not appear to have any lateral play in it.
For the entire episode of hard starting, I seemed to be getting poor spark to the points.

Yesterday, I installed a Pertronix 40111 epoxy coil (https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1), and the car began to start reliably again (hot and cold), even with the tachometer connected to both sides of the coil. Installing the Pertronix coil was the final change I made. So, it's higher output appears to be allowing the engine to start reliably again.

So, I’m wondering if a bad tachometer could make a Model A hard to start. Could the tachometer be robbing the other coils of enough of their power so that the points do not get enough spark to fire the engine?

12-11-2020, 07:04 PM	#1
shew01 Senior Member Join Date: Sep 2016 Location: Roanoke, VA USA Posts: 1,908	Could a bad tachometer make a Model A hard to start? I’m still learning about the Model A ignition system (and tachometers, for that matter), and I’m wondering if a bad tachometer could make a Model A hard to start. Here is some background information. Around the beginning of November, I noticed that my tachometer (https://www.westach.com/product-page/2ct32-6v), purchased new in May of 2020, was acting flakey from time to time. (From May to October, the tachometer worked fine.) While idling at a stop light, sometimes the needle would “float” high, but there was no corresponding change in the engine sound, and then the needle would eventually drift back to 500-700 RPM or so, again without any change in the engine sound, meaning that the RPM sounded constant, but the tachometer erroneously indicated a change in RPM. Also, while driving at what was likely to be 1500 to 1800 RPM, the needle would sometimes waft up to 2200 to 2500 RPM, with no perceptible change in the engine sound. Apparently, the tachometer sometimes has a mind of its own and displays whatever it wants to display. The unit appears to be under warranty; so, I need to call about it. However, I’m curious. For the last couple of weeks, the car has been uncharacteristically hard to start. (https://www.fordbarn.com/forum/showthread.php?t=289945) I’ve jumpered the junction box posts together to take the ammeter out of the equation as a potential problem. I’ve tried a number of different coils (two oil filled coils and one Ford script coil) and two condensers. I’ve thought I had the problem solved a number of times, but the car would continually “backslide” into hard starting over the course of a couple of days. I have observed the following while working through this issue. I‘ve used a Sparklite (https://www.brattons.com/ignition-sp...il-tester.html) a number of times when cranking the engine, and I’ve noticed that the engine does not “catch” unless there is a fairly bright LED flash at some point from the Sparklite. (A weak spark sends no flash to the LED or just a faint flash to the LED.) When the car did “catch,” I would always see a strong LED flash from the Sparklite as the engine "caught," and a strong LED flash would continue while the engine was running. The engine is hard to start with or without the Sparklite connected. So, the Sparklite does not seem to be causing any of the problem. Not considering that the tachometer could be a potential problem (until now), I’ve always connected the tachometer to both terminals of whatever coil I’ve had in place. Regardless of the coils and condensers, the car would still be hard to start at some point, regardless of whether the engine was hot or cold. I’ve checked the points a number of times, and they are set at .018. The distributor shaft does not appear to have any lateral play in it. For the entire episode of hard starting, I seemed to be getting poor spark to the points. Yesterday, I installed a Pertronix 40111 epoxy coil (https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1), and the car began to start reliably again (hot and cold), even with the tachometer connected to both sides of the coil. Installing the Pertronix coil was the final change I made. So, it's higher output appears to be allowing the engine to start reliably again. So, I’m wondering if a bad tachometer could make a Model A hard to start. Could the tachometer be robbing the other coils of enough of their power so that the points do not get enough spark to fire the engine?