Is the pedal adjusted right, will it bring the MC plunger all the way back when the pedal is at the top of it's travel?
One way to check is see if you can wiggle the linkage at some point near the top of the pedal travel. If you can't then likely the MC plunger never fully retracts and the linkage needs to be shorter.
Hard to explain, but hope it helps,
Grigg
