1992 Toyota Tercel 1992 Toyota Tercel 1.5 motor low commpr

1992 Toyota Tercel 177896 miles

i have a 1992 toyota tercel with a 1.5 motor. Motor was replace a bout 30,000 miles a go.# 1 cyl is 100.#2 is 50.#3 is 140. #4 is 120. I aslo done a wet down test and was no change in the cly.. I was told it might be a head gasget. Or could it be a burt vavle. Thanks. Note car still runs and drive. Not very good gas milage . Thanks again