<VV> Spyder Tach and Crane Cams XR-700 Electronic Ignition

[Jim]

Recently, I replaced the engine in my '64 Spyder with newly rebuilt one [Hi,
Tim!].  It came with a Crane Cams XR-700 ignition.  As it happens, my old
engine had an Allison XR-700 ignition, which I think is the predecessor to
the Crane model.  The pick up and wiring are the same.  Here's my problem:
The tach reads about 250 RPM low at idle and about 1000 RPM or more low at
highway speeds with the Crane.  It worked normally with the Allison.
 
Any thoughts about why this is happening?
 
Jim Bartasevich
'61 Lakewood, 140/4
'64 Spyder convertible, 180
'69 500 110 PG
 
Such is the human race.  Often it does seem such a pity that Noah didn't
miss the boat. - Mark Twain