Timing Light Accuracy

I have the same light. I have been using it for 40 years, only thing I have ever had to do was re-solder a joint inside.

if you want to do a rough calibration / check, find a computer controlled car and check its advance. this may or may not work. I had an older car that I could do this with.

mopowers said

Maybe this 340 just an anomaly because it seems to want 30* initial adv.

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I would think you have other problems like no vacuum advance?