Quoted from AUKraut:
Sounds like you have it 180 degrees out of phase, i.e. you got the orientation for it shooting into the upper playfield shooting to the lower playfield (and vice versa). Turn the whole assembly by 180 degrees.
I think we have a winner! There's 2 different coils installed on that mech, one is considerably stronger than the other--the stronger coil is to send the ball to the upper pf, and the other one is weaker since it's sending the ball down the pf (which requires a lot less oomph)