<VV> Spyder Tach and XR700 ignition

[James Davis]

The Corvair tach basically integrates the dwell time of the coil over a
fixed time interval.  That is why the tach's signal wire is attached to the
ground side of the coil. For instance, at 600 rpm there are 30 dwell pulses
per second.  It is just an electrical analog of a digital computer with an
analog display.   If the dwell time changes from the desired 31 degrees the
tach will read incorrectly.  For those of us that run points, the bouncing
tach needle indicates the points are closing up and and need to be recapped
hopefully with a handy dwell meter.
Jim Davis

On Wed, Jun 1, 2022 at 5:13 PM Colin via VirtualVairs <
virtualvairs at corvair.org> wrote:

> Could your problem with the tacho reading low be related to the ignition
> being set up for 8 cylinders whereas it is receiving pulses from 6
> cylinders. May be there is a switch on the XR700 unit that switches between
> 4, 6 and 8 cylinder applications?
>
> Colin LYNN   28299
>
> Perth, Western Australia
>
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