Not sure you are having the same problem that I have with many/most of my Narrow Frame hydros or not.
Go here and check out the exploded view.
http://www.partstree.com/parts/?lc=c...&dn=0018900011
Usually when I get a Narrow Frame hydro parts #15 and #29 are badly worn and prevent the pedal from bringing the control lever back to center. So I replace the pin (#15) and file then sand/emery the angle portion of part #29 until it is as smooth as I can get it, I also "round off" the sharp corners on the angular area so they don't "dig into" the new pin and cause more than necessary wear.
However with the ones I've had they don't want to come back to center no matter what the operating temp. is or how long/short I've had them running.
Good luck getting it figured out.