[Mgs] Unsteady timing

[Ron Fine]

I am having a problem setting the timing on my newly rebuild engine.  It seems
to jump around plus or minus 5 degrees.  I am using a new digital adjustable
timing light.  The distributor is new (Moss) 45D4 replacement for the original
25D.  The vacuum advance has been disconnected.  The cam is new.  I did a
static timing when setting up the engine and it has been running well for the
first 300 miles but running hot.  I tried to adjust the timing today with the
new timing light but with the idle between 800 and 1000 rpm the timing mark is
jumping between 0 and 5 degrees BTDC.  I can't get it to idle any lower
although the book says to set the timing at 600 rpm 14 degrees BTDC.  Any idea
what might be the problem?  Is it possible that the new distributor is
faulty??   I also installed a new coil and new plug wires with the new
distributor.  The points were adjusted on my bench before installing the
distributor, so I believe they are set correctly.
Any help is always appreciated.

Ron Fine
66 MGB
61 BN7