I'm pretty well stumped.
My racing Spitfire has a MSD ignition system using a point driven
distributor.
I have new high tension wires with 4 ohms per foot resistance.
The following observations are made with a timing light.
1) With the timing light power taken from any convenient point in the
engine compartment and a convenient ground, with the timing sensor on
the number one wire, the timing light shows the timing is set right, it
also shows abundant other flashes, most notable at roughly 90 degrees
from that of the number 1 plug. Interesting enough I get the same
pattern of flashes when I take the sensor off the number 1 plug and hold
it 6 feet away from the car. All I need to do is power and ground the
light from the engine compartment.
2) I get the same abundant flashes with or without the sensor being
connected when I use an engine ground and power directly from the
battery, or connect the timing light ground to the negative pole of the
battery and pick up the hot lead from the engine compartment. In both
cases 1 and 2 I get the same pattern of flashes with and without the
sensor and with the sensor on any high voltage wire, plug or coil.
3) However, if I connect both the power leads to the timing light
directly to battery I get no flashes until I put the sensor on a plug
wire and then I only get flashes where they belong, no extras. On time
for plug one and rotated appropriately for the other plugs.
I have tried to isolate the ignition circuit from the rest of the car by
using separate grounds for everything else, one exception comes to mind
is the brake lights. On a racing spitfire the isolation is not
insurmountable but things keep sneaking up on you.
I consider this to be bizarre. It may not really effect the plugs firing
( see observation 3 ) but it seems as though the ignition is causing
some sort of power fluctuation in the 12 volt system of the car and that
the battery can damp it out. However, the car does not seem to run quite
as crisply as I would like and the power fluctuations in the 12 volt
system can't be helping matters.
Any suggestions.
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