360 hesitation and

What was at TDC?
I think what YR is asking is; Is the TDC mark on the balancer known to be correct.If you do not know, then you should prove it, because if you don't, then the ignition timing could be in error, and there is no way of estimating how far out it is.
And one of the comments you made earlier pointed to a possible erroneous timing setting.
This one from post #10
Well I added some dry gas thinking possibly moisture in the gas, no luck. Below is the picture of one of the plugs, they look fine. No matter where I set the timing 0*-5*-10*- 20* it runs best around 10* but I still am getting the back fire under load. Could the carb be bad from sitting 2 months dry? I know AJ is saying clean it, does that mean rebuild it? \ \
This is unusual.
Are you saying it idles best at 10*
or backfires the least at 10*
or something else?