if it's sputtering, that surely means that your cupseal on your valve is broken.
It's a very simple fix. Just open up the lower tube, remove internals down to the valve, swap valve stem/cupseals, cake the seal in grease and then replace all internals and close it up.
ANd yes, lube your bolt, but the lubricant CAN NOT be water based or petroleum based or it shall swell and destroy your bolt along with wearing out your breech much quicker.
Lubing the bolt aids in consistecy, sealing off the breech better, and ensuring that there's minimum blowby.
note: azodin and spyder valves are prone to this issue as well. Consider upgrading the valve for a lower operating pressure, better consistency and efficiency, improved sound signature and smoothness and a more reliable gun.
AKA 11/16ths valve would be my go-to preference, followed by the Maddmann rocket and then the NDZ SS LP valve.