Coil making a weird buzzing sound

[Marty Rogan]

While starting my '71 the other day, I heard a loud pop, saw a puff of smoke over the intake area. I also smelled burnt wiring. Looked all over, but could not find any burnt wires. My MSD coild was making a really weird noise, even after I had disconnected the battery. I figured the coil must have fried, so I replaced it, and the new coil is making a buzzing noise too.

Also, when you rev the car above 3k, the tach momentarily drops to zero, then bounces back. I am sure that is related to what is going on in the coil.

I am using a Pertronix. Everything else is stock '71.

Any ideas on where to look into this?

TIA,

Marty

[=Enigma=]

That's jsut scary. Don't stand too close in case it bursts on you. Hot oil is not a very nice thing to have sprayed on you or in your eyes. I have no idea what could cause that but hopefully someone can help. I'd check for a short somewhere. Perhaps the low side terminals are shorting out or something like that?

[Marty Rogan]

Update on the coil buzzing. I still have not found the actual cause of the buzzing. One gearhead buddy said that it is likely the oil inside boiling from overheating.

I changed the ballast resistor and so far it seems that the buzzing has stopped. My tach still drops off after revving up to about 5700.

I have checked all the wiring and the grounds look good.

Any ideas on why the tach drops off?

TIA,

Marty

[Marty Rogan]

Here's the resolution to close this one out.

The new ballast resistor has seemed to fix the buzzing sound.

Over the weekend, I pulled the optical sensor in dizzy to clean it. Three of the magnets fell out of their slots. I put in a spare that I had and the tach now pulls smoothly to 6K. So if you see this issue, clean the sensor and check the magnets.

Marty