Dang Mysterious Electrons…

[Oiluj]

OK, here’s an interesting observation / dilemma.

I have a strut brace-bar in my engine bay, the typical round, chrome bar as sold by MSA. (attached pic)

When adjusting the idle on my front carb, the screwdriver shank contacts the strut bar, making a metal-to-metal contact.

When adjusting my idle speed the other day, I noticed a weak “ignition spark” from my screwdriver tip to the idle screw, just before it touches.

So it looks like I have a high voltage leak somewhere in the ignition system, but can’t find it.

At first I thought the ignition wires were to blame, but it happens with both my old and new ignition wire sets. I’ve verified that the high voltage ignition wires are not contacting metal anywhere, and are at least 1/4” from any grounded metal surface. Same for the high voltage wire from the coil to distributor.

Further, I can grab any of the ignition wires without feeling a jolt. - (Dumb mech engr type of test). After all, if I can’t see the electrons, they don’t exist and can't hurt me, right?

Any thoughts on what to look at next?

[Zed Head]

OK, here’s an interesting observation / dilemma.

I have a strut brace-bar in my engine bay, the typical round, chrome bar as sold by MSA. (attached pic)

When adjusting the idle on my front carb, the screwdriver shank contacts the strut bar, making a metal-to-metal contact.

When adjusting my idle speed the other day, I noticed a weak “ignition spark” from my screwdriver tip to the idle screw, just before it touches.

So it looks like I have a high voltage leak somewhere in the ignition system, but can’t find it.

At first I thought the ignition wires were to blame, but it happens with both my old and new ignition wire sets. I’ve verified that the high voltage ignition wires are not contacting metal anywhere, and are at least 1/4” from any grounded metal surface. Same for the high voltage wire from the coil to distributor.

Further, I can grab any of the ignition wires without feeling a jolt. - (Dumb mech engr type of test). After all, if I can’t see the electrons, they don’t exist and can't hurt me, right?

Any thoughts on what to look at next?

You are probably supplying another ground path to the battery, through the brace to the mounting points, then on to the negative terminal of the battery. You might have a weak ground wire connection or corroded connection points. I think that the sparks imply that there is some resistance in your current ground path, from the engine to the battery.

The main ground for the engine on my car is from the negative terminal of the battery through the heavy gauge wire to a transmission mounting bolt. It would be worth checking yours to make sure it is low resistance.

[Oiluj]

OK, that makes sense... I had considered it might be a ground problem, but hadn't fully thought it through as you did.

I'll check that out this weekend. Thanks for the input!

[rv6aflyer]

Usually a weak ground will really hurt your starting performance. If the car turns over nicely, you probably have a good ground between the battery negative and the starter motor, which is usually grounded through the engine. If you don't have one, buy yourself a cheap voltmeter. Harbor Freight often has them on sale for $2. With the engine not running, but the ignition on, set the meter to 20V DC and measure the voltage between the two points the screwdriver touches. If you see ~12 volts, you have some "loose" electrons. Both points should be ground, so measure between the battery negative and both locations to see which one is "hot", likely the idle screw. Now try to find how the voltage is getting to the "hot" spot. Unhook any electrical connections one by one and repeat the test. If it is truly high voltage from your ignition system, it will only be there when the engine is running and would normally continue to be there as long as the screwdriver doesn't touch the idle screw, just is close, kind of like a sparkplug gap.

Hope this helps.

[Gary in NJ]

Nice write-up rv6a. That's a very logical procedure.