1: The Gun has a built-in stall feature to prevent overloading. Try reducing the piston speed as shown on page 5 of the Dosing Gun Manual 2: Remove the barrel and valves (inlet and outlet) and make sure everything is clean and moves freely. 3: Check the drive thread. Remove the barrel and pull the trigger and see if the gun stalls. If it stalls without the barrel it could be a tight drive thread. The drive thread is self-lubricating however a small drop of oil could help. If the drive thread is tight and makes the motor labour then the drive thread and piston should be replaced. 4: Check that your injection site is correct. The gun may stall if the needle hits a bone.  5: If the Gun still stalls then take note of where the piston is stalling and contact Te Pari. If it is stalling on the return stroke there could be an issue with the magnet sensor in the piston which detects the home position. Contact Te Pari for support.