2 minutes ago, cclxxxz said:

how would you calibrate a tach ? i would imagine i would need another tool ?

Maybe Zed or someone can back me up, but I thought there was a small screw on the back of the tach. I would try to adjust it with the car idling and see if I could get the tach to show an rpm at idle.

If I could, then use a timing light with an rpm display to try to get it adjusted properly. After calibrating the idle rpm, check the tach versus the timing light at a few different rpm's for confirmation

1 minute ago, Patcon said:

Maybe Zed or someone can back me up, but I thought there was a small screw on the back of the tach. I would try to adjust it with the car idling and see if I could get the tach to show an rpm at idle.

If I could, then use a timing light with an rpm display to try to get it adjusted properly. After calibrating the idle rpm, check the tach versus the timing light at a few different rpm's for confirmation

will do it.. gonna buy a dwell/tach tester and try calibrating it.. thanks!

I've never adjusted a tach.  I do remember trying to turn some of the screws in the back of a tach and they wouldn't budge.

I would try putting the stock coil back on.  That 0.6 ohm coil might be affecting the tach.  I don't really know what the tach "sees", if it's a flyback thing or a low-high voltage thing.  But I do know that ignition system modifications can affect the tach operation.

Plus the 0.6 ohm coil is letting more current through your 40 year old ignition module.  Not going to add to its probably short life remaining.

7 minutes ago, Zed Head said:

I've never adjusted a tach.  I do remember trying to turn some of the screws in the back of a tach and they wouldn't budge.

I would try putting the stock coil back on.  That 0.6 ohm coil might be affecting the tach.  I don't really know what the tach "sees", if it's a flyback thing or a low-high voltage thing.  But I do know that ignition system modifications can affect the tach operation.

Plus the 0.6 ohm coil is letting more current through your 40 year old ignition module.  Not going to add to its probably short life remaining.

will try to switch the ignition coil back also.. and see what happens...

 

then maybe itll be time to switch the GM HEI MODULE.. haha

Edited March 3, 20196 yr by cclxxxz