FX FX Wildcat MKl tuning help

Hey all, I have an fx wc mkl in .25 that I would like to tune to shoot jsb 33.95 gr pellets. I have searched yt high and low and can't find any help. Anyone here with some knowledge that can help me out. I shot them today and they are shooting 780 fps. I'm thinking I need to be around 850-900 fps, I don't know how to increase my fps on a mkl. Thanks in advance, Jamie