Fluctuating neg. to ground on ignition coil

Mattax said

It depends, but if I recall the previous posts, this is a stock 1978 360.
We're seeing idle fluctuating between 1250 and 1500 rpm. The movement of 250 rpm is a little more than I'd like to see but not surprising in conjunction with your other observations.
That isn't the correct slow idle speed though. It might be correct for an engine warming up after kicking it down to the 1st step.
Has the AIR injection tubing been fixed or plugged?

Click to expand...

The the tachometer is for 4 cylinder engines and the reading should be multiplied by 0,5 to get 8 cylinder figures, which would be 650-750 that it is, so the movement is approx 125 rpm measured, it does not change that much in reality, just the tachometer which made me curious why it does.

The AIR injection has been taped closed temporarily.

I have looked down the carb with a flashlight at idle, and it looks dry from above, no fuel dripping visible.