this is not getting the amount of fuel ,or spark when needed.
it fires sometime which means it has a dirty contact somewhere.
u need to find it and clean it good.
the entire gun comes apart,and clean piston,ignition area,spark ,trigger,remove o ring on fan area and clean, then lubricate with only paslode oil.
when cleaning ,let all the dirty crap run out of gun dont let it stay inside.wipe clean with rags.
oil up o ring and all the cylinder area.push piston down and lube good.