71 LA 340 timings moved!! how?? looking for help

Shane pearce said

Also I'm assuming its not stuck as it advances instantly with a bit of a rev, I saw 40... but didn't risk anymore as I just dont know where it should be, I was thinking around 16 -18 degrees????

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That is not what is being said. There are 2 advance mechanisms: mechanical and vacuum. What it being suggested is that the vacuum advance mechanism has broken on some odd fashion and is jammed and that is starting the total ignition advance at a very high number. That could happen, and the mechanical advance would still work... which is what you are seeing when you rev it some.

And yeah you had better back the way back down I would start in the 10-15 range with your high static CR; looking at your engine parts, SCR computes out to around 10.6 and could be more. And the DCR is in the mid 8's and that is pretty darned high for iron heads. No wonder it was carrying on... it was very, very likely to have been detonating, IMHO.