Quoted from MajorDrainer:I've heard several fixes for plunger problem. What worked for you? If you bought new plunger spring, what size and where did you buy it? Thanks.
First, you want to confirm whether the auto launch forks are sitting evenly on the ball. If they aren't, gently bend them with pliers to where they are. If the forks are sitting correctly on the ball and the manual plunger still isn't strong enough for your liking, change out the shooter rod spring for a "red" spring. Marco and Pinball Life carry them.