Bouncing Tach?
 

My car is new to me - 1974 911

The tach bounces about 2000-3000 rpm between shifts, without the engine actually reving. I know there was a thred about this on the 914 board but I cannot find it.

Any advice would be appreciated.

Could be a few things, voltage spikes (check VR), short in wiring (check wire from distributor), but it my case it was a worn set of points. I would start there....

Same problem with a Pertronix ingnitor. Distributer clean and lube fixed it. Probably a grounding issue.

In my case, a bouncing tack has always meant the points were failing. Does the tach bounce while at a set rpm?

Points, grounds, tach. Don't forget to pull the tach and clean all connections if points are ok.

The tach is stable at idle and while driving. It only bounces between shifts.

I will take all the advice and cleant things up. I've only had the car for two weeks and althouh it's very clean (inside & out), I have yet to fiddle with anything in the engine compartment.

Putting on a new roof on my house has given me no time for cars, this week.

I've got a newer alternator and electrical system thanks to a fire mishap and my tach still does this even after the rebuild. I would seem that based on posts here that the damper fluid/damper something inside the tach is worn out. There are some success stories here about sending it out to be repaired and then no more bounce.

..not to hijack this thread but what about on an 87? Mine flickers at around 3400 rpm when cruising...no other rpm, just this one......I have no points see?