sounds like your engine needs a valve job
worn piston rings would also cause low compression ,but not cause the backfireing
Mine is in great shape, '03 Buyou 300 4x4. Cranking compression w/good battery and starter is 160lbs after 4-5 compression strokes.
160lbs
160lbs / 2.2 = 72.7272kg 1 liter water = 1 kilogram =72.7272L
160lbs
160lbs
160lbs
160lbs
130-160lbs
I think about 160lbs
160 pounds = 72.5747792 kilograms
About 712 newtons per 160lbs.
qb