Just picked-up a Cen-Tech timing light (Model 40963) from Harbor Freight. the light works well enough in that it's bright enough to see marks during the day. (Apparently some are not.) It has an adjustment on the back to check timing advance. (Up to 60 deg.) A handy feature, I suppose.

So, here's the deal: the dial can also be turned past "0" into the "negative" realm. Of course, the flywheel mark and indicated engine timing move too - indicating retarded or less advance timing. I've set the light to "0" and set the timing accordingly and everything seems OK.

But what if "0" were not actually zero? How would I know? I mean a couple degrees here, a couple degrees there, one could argue that it matters not. But if I'm taking the time to set it, I'd like to be reasonably confident that it's close.

Any thoughts?

clk

 

I got the same one. Kind of wondering about its accuracy as well. Thinking about returning it, and getting the Equus 355. Doesn't have a dial so you don't have to worry about it.