Tacho mystery

[88v8]

My 327 has a rev counter, fitted from new. Runs off the coil neg.
Never seemed that accurate although as I (still) haven't driven the car yet, hadn't paid too much attention.

I'm sitting in the car yesterday running the engine, hoping I've got to the end of the problems and can take it out for a run, but no. As I rev up to about 2,000 there's a bad misfire. Shakes the engine. If I try to rev through it, I can and it clears, but while it's missing it's pretty bad.

Then I notice that the rev counter stops rising at the point where the misfire starts, and when it gets bad the needle goes all the way back to zero.
I tried disconnecting the rev counter in case it's somehow causing a problem, no change.

Misfires hot or cold.
Timing is OK plugs are new, firing order is right, points gap is OK. Original coil & ballast, the coil impedance is OK for the ballast. Fuel pressure is correct, I set the wet fuel level.

I'm inclined to replace coil and ballast, but I don't like randomly replacing things.
So, do you think the rev counter is trying to tell me something about the ignition, or is it just faulty?

Ivor

[ex-tyke]

Running points?.......could it be something simple like a condenser?

[kstevusa]

Perhaps a check to insure the GROUNDS are secure.  Battery(rear) to body, body to drive train and drive train back to body at engine. Brit cars tend to have a few  glitches  and most I've had were related to the Poor Grounds, earths .

[BlownMGB-V8]

That symptom is pretty typical for dirty points or coil breakdown. Possibly condenser. The tach is trying to tell you it needs a tune-up.

Jim