[Zfurlong]

There are a few possibilities, with the first being arcing between your trigger contacts. Your p90 should be a 2 stage trigger when set to full auto, with a partial squeeze being semi and full squeeze pushing full auto. The most common issue is arcing between the contacts and all that would require is a cleaning of the contacts themselves. Another possibility is the contacts being separated too much which can be finicky to reset them back to normal. If your p90 is in fact set up on a micro switch, it's possible the spring for resetting the switch is faulty. My best recommendation overall would actually be swapping the innards for a complete hpa build. Makes things a bit easier in terms of tech work.