[Synchro909]

I used the fact that the distributor could be turned to get the timing in one of my cars right. I initially set it as per the book but it was too far advanced and would ping under load. I gradually backed it off till the pinging disappeared. It might be a little retarded at an idle now but that causes no damage, after all, it's only idling for a short time now and then. I think I have the sweet spot because it runs REALLY well. As I type this, I've taken a break from reassembling things after replacing a head gasket (caused by a "leakless" water pump leaking). I have noted where the distributor fires on the timing scale on the front of the block at idle and I'll set it there again in a few minutes. Should be just as good as before but if not, I'll just do the same gradual adjustments as before.
The amount of advance your motor needs changes as you change things like camshaft timing, compression ratio, fuel and carburettor. If you've changed any of these, it may not be good enough to set the timing by the book.