If the manual hydraulic stacker does not rise slowly before refueling, and it rises slowly after refueling, one may be that the air is not exhausted. Released the throttle switch, put the fork at the lowest level, pressing about 20 times until the air is exhausted, and then tighten the throttle switch to test it.
Another reason may be that the oil is too thick. The simple way to eliminate it is to put the forklift in a greenhouse and check the situation the next day. If the rising speed becomes faster, it can be definitely the cause of oil thickness. The solution is to replace the 32 # hydraulic oil or use the 8 # hydraulic transmission oil.