I'd check the air lines to make sure there are no obstructions and the lines are routed correctly. try disconnecting one side of the air lines and operate. Then as LiveWire suggested check your air valve. it has to be positioned correctly to make sure pressure goes to either the extend or retract position. Finally check to make sure that the vent on the retract valve is open. Again as LiveWire suggested the vent port on the valve may be closed. open them up wide open and then slowly close to get the desired retract or extend speed. Remember to set this a little higher then expected. With the airplane flying the gear will be working against the air loads.

adding link to instructions. Checkout section 6 for troubleshooting....

Cheers,