Decided to change out my points to pertronix lobe sensing on my 67. On first startup timing was way advanced and knocking at idle. Ran good before no problems. Retarded timing using my dial back light to 46 deg total (vac adv, everything) and it backfired bad upon rev up. Went to 50 deg total and it was better but still not like before. That seems like a ton of timing to me and I wish I had checked it before the swap but I never thought it would advance just from the swap. The pertronix will only install in 1 spot so I know it's located right. The engine is pretty much a stock 326 ho w/ stock carb, distributor, intake. I've read for hours and need some direction. Everything I've read on Pontiacs says 46-48 is about max but it seems like this thing wants 52-54 degrees. Is it possible?