273 super commando #4 and #6 not firing

I bought a 67 Coronet with a teen years ago. It barely made it home. I tuned it up and it still ran like crap. I warmed up the engine and trickled a pop bottle full of water down the carb. It blasted the carbon from the valves and it ran great. It was my daily driver for a couple years. Apparently the previous owner drove it for too long with a couple cylinders misfiring and carboned the thing up.
Note: I trickled not poured water down the carb. I would use a carbon blaster product available today. You might want to try it. tmm