How many RPM are you turning on takeoff?? Just for comparison, on my 582 powered avid, with the prop set for cruise ( IVO IFA 72") I will only turn 48-5200 on take off on floats and it will not get on step. With the IFA I can flatten it out and turn 6500 and then feed in pitch to keep the RPM and EGT under control as I gain speed. If it is the old style amphib gear, I would not use them for much more than beaching.. The 1220 are a little small for the KF or Avid and the 1450 work MUCH better!