Nikoo

Hi, I just bought a WE hi capa 5.1 and I tried to convert to hpa but the nozzle stays in the forward position when firing. It does work if I manually pull the slide back. My only guess is either the nozzle is damaged (but it works with green gas) or maybe the previous owner put too many spacer with the short trike kit. im new to hpa and pistols only ever had aegs so any help would be very appreciated. thanks.