G&G RK-47 hopup

[MADMAN983]

i reacently aquired a brand new G&G AK and its awsome with 1 minor flaw, the hoppup is inconsistant, some shots overhop, others underhop, the hopup slider isnt moving so im assuming its a problem with the hopup.
should i replace the hop with a better one?
i have used to gun for 3 games with no noticable change to the hop so letting it "were in" didnt work