318 Running Richer w/ Carb Swap

I took it for another run and gave it a good hit but went for a run around the back woods with a ,mate to show him the power of the 410 and give it a hit in second gear. Well it did its usual 6000 rev sideways action but pulled a big back fi while doing it.
I had a think about it and the only thi run. ng I had done was to open the plug gaps.I took it for another drive and gave it a hit but it back fired at the top end badly so I returned home and closed the gaps on the plugs to about 40 thou than took it for another run. The engine pulled to 6500 with no complaints.
So maybe as low compressuon engines like the old side valve six that my brother said ran the best it ever had with really big plug gaps, but a 11.5 comp 410 small block did not like it even with an 8 amp ignition system.