another valve question

[cosworth34677]

hey i got a problem with my excavator . my mangom valves seem to work great. but the servos act like there is not enough throw to open the valve fully in the retract direction, i have tried to cent er servo with the trim and by taking off the servo horn but it seems nothing is working to get the center in the right place to have even movement in both directions?

so being me, i was wondering if there is a trick to this setup? i mean when the boom goes up its at full power and crazy strong but when it goes down its slow and have less then half power. what im wondering if there is something in the valve clogging them ? but if i take the servo off and move the valve by hand it works fine, but when put the servo on it back to the problem. i even went and got a new set of servo's today the stick and bucket work great its just the boom. what of any idea's can help me?