Timing Light Accuracy

yellow rose said

That's OK because the HEI will retard with RPM too. You can't see it with a timing light but you damn sure see it with a good distributor machine. That's why locking out the timing is a bad deal.

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Sorry not correct. If a timing light does not move, then neither did the timing. I DO NOT trust "dial up" lights. I've seen at least 3 over the many years, that were not accurate for some reason. I have two very old Craftsman "Roger Penske" lights, one is direct wired, and one is an inductive, both look identical from the mid -70's

If you have some test setup that shows the dist. changing and the timing doesn't then it is changing "in the box"