<VV> What is Dwell?

[Smitty]

Smitty says;  As a straightforward answer to Jeff's straightforward 
question, can you have too much dwell.  Yes you can.
I offer this short tutorial.  When a coil such as the one in your ignition 
receives a charge of DC the, coil absorbs the charge and being a 
transformer, kicks the voltage way up in the secondary windings.  (The ones 
feeding your plugs).  The coil reaches a point of saturation but immediately 
the voltage starts to decay.  It can not be maintained by DC.
The engineers have calculated how long it takes,from when the points close, 
for the charge to build up to that peak.  Then they design the distributor 
make the points snap open which releases the built up charge from the coil. 
If the points stay closed too long the decay will take place too long and 
the stored voltage will drop off to nothing.  That "charge up"time is called 
dwell.  (The period of time the points dwell together).
The engineers had to make an educated guess on how much dwell to set up when 
adjusting the points to satisfy the needs of the engine from 500 rpm to 
7,000 rpm.  Obviously there isn't much dwell at high RPM and way too much at 
Idle, so they made a best guess and gave it a number.  First indication of 
too much dwell ( points too close ) is hard starting.