74 2.0L duel carbs
Car runs good, while racing around the neighborhood I noticed my rpm's were low, not getting over 3K. But, sounded/shifting normal.

Was positive at least around 3.5K-4K

Hooked up my dwell/rpm/volt meter and yes, was rpm'ing properly.
But, the tach was not indicating correctly.

Does a tach fail slowly?
Your thoughts.

Thanks!

Anything with electronics in it can get out of spec with age/usage. Resistors break down and their values change, capacitors start leaking, etc.

The tach in the 'BB' is intermittent, but I think my problem is a bad (loose) ground ... the terminals at the coil and at the back of the tach are OK.