Yesterday I ran some tests to characterize the spark advance - engine revs curve with a dial back timing light using the OE US model 750 ohm resistor and zero (shorted the plug) and infinite (removed the resistor) resistance.

The shorted plug case is supposed to represent the least rate of advance and least total advance, and the open circuit case the highest advance rate and most total advance.

For all cases the initial timing was 9 and the vacuum line to the EZL module was removed and plugged, but prior tests indicated maximum vacuum advance of 14 degrees.

Figure reading error is plus/minus one degree and 100 revs, but might be a little more at high revs since the mark tended to jump around a little more.

750 ohm OE resistor:
17@1500
21@2000
27@2500 (maximum)
27@3000
27@3500

Zero ohm - plug shorted
09@1500
13@2000
18@2500
19@3500
21@4000 (maximum)

Infinite ohm - open circuit
16@1500
21@2000
27@2500
28@3500 (maximum)

It's possible that once the bulk of timing is in the advance continues to increase at a very low rate to higher revs, but it is difficult to discern.

The resistor is still out, but I haven't noticed a SOTP improvement in performance that has been reported in other discussions.

If anyone else can run a similar test, it would be nice to have another data set as a sanity check.

Duke