318 backfired and now runs like it has a misfire

idle the engine at 1000 rpms then pull each wire off one at a time if the engine is shaking the bad cylinder will smooth out when the wire is pulled.(intake valve not closing right ,carbon on seat ect) your looking for a drop of 50 rpms each cylinder with wire off this was referred to as a cylinder balance test back in the day, but if you have a compression tester that's where you start like all the other have said. DID YOU BLOW OF A VACUUM LINE WHEN IT BACKFIRED? DID YOU PUMP UP A LIFTER THAT WONT BLEED DOWN?