Jabba,
Make sure the plastic finger that comes down through the playfield and activates the switch is centered in the switch "spoon" and that the switch is square to it. You can run your switch contacts very close together on pop bumpers, you'll know when it's too close when the bumper fires twice in a row or fires when another bumper is hit. Not much more I can tell you, just messing around with it for awhile to get it just right is sometimes what it takes. Generally either the coils works, or it doesn't, so I doubt you have a problem with the coil itself. The circuit is pretty much limited to the switch and coil, so you shouldn't have to look any further.
And, um.. yes, that's the storage area.... I run a small arcade location on the side plus I do work for an op, so it's not all "mine"...
D