ther are a couple of things that need to be looked at first.
make sure fuel cell top is popped in all the way.
red nozzle in gun is facing the correct way.
gun should fire .
if not this gun is very dirty inside and needs to have the ignighter area cleaned really good.
read your manual on disassembly of the unit and this will work.
iv repaired many guns,and this iswhat needs to be done with yours ,since your gun fires sometimes.
tool repair ron