We had that problem on a Ferris last year. Our problem turned out to be bad linkage. Each point in the linkage that contected to another link adds to the the total play in the linkage. Check each and ever link from the handle to the pump in vlave shaft. Try this, hold the valve shaft and have some one real slow like move the handle and see how far the handle moves before the valve control shaft does. You May be surprised. On the Ferris even after we put new linkage on it Ferris sent us a set of small shocks (Gas Springs) to help control the hopping. Good Luck
"DEFECTIVE OWNER/OPERATOR NOT COVERED UNDER WARRANTY"