Question? Timing problem on an older smallblock chevy 350

Truck runs better with the timing advanced high at the distributor instead of the normal 6-8 degrees. when it was at 8 degrees it ran fine until the engine got warm then it would start to back fire up through the carb if there was any kind of load put on the engine. Any ideas to what they problem could be? or how to fix it? thanks

is you distributor a hei or points? if its HEI, I got backfire really bad...to the point of exploding my muffler...I replaced my HEI coil. other than that maybe your timing chain is loose. how long since thats been replaced?

Anyone else to help this poor soul?