12 degs is less than 16 degs and that is considered retarding the timing...going from larger to less.
If you have 16 degs of timing for initial and something like 36 degs for total, then I strongly doubt that any heating problem is due to timing.
If you have the vacuum advance connected, then you can plug the port on the carb so it cannot work and see if that makes a difference. I doubt it will unless you are running a ton of vacuum advance.