Joe,
Do you mean by detonation sound blast out the tail pipe? Or is it like having a wire on the wrong cylinder? I guess that these two situations are too close to be distinguishable, but I guess I am trying to understand if it's detonation or backfire out of the carburator.
If you have an initial of 12 deg BTDC, then if the weights are hanging up, then you should not be able to see a whole lot of the timing advancing above idle with a timing light. Does the detonation reduces if you set an initial of 15 or even 17 deg BTDC? By the way, one has to check the weight's movement carefully. It may seem like they're not hanging-up on anything, but it usually does hang-up. Like the plastic buttons they brush against. One weight post could be slightly bent as well.
The pinging sound you hearing reminds me of the power tuning for a vacume advance. You give it a little more until it pings, and then one reduces the rate at which the spring in the vacume cannister moves (counterclockwise, I believe). However, this is possible on an adjustable cannister or like Jack says, a pin hole in the diaphragm. So your vacume advance is momentarily too much (once the carb is WOT, the effect of vacume-operated advance mechanism is almost entirely eliminated).
