Diagram of Hitachi NV 83 a nail feeder - Hitachi Tools & Hardware - Others

SOURCE: i have a hitachi nv 65 ah that will shoot two

I hope this doesn't offend you. What I'm suggesting is that you may not be using your nail gun correctly. Some people keep the trigger pulled and bounce the gun onto the wood. This technique works okay, but placement accuracy of the nail suffers. The other technique is to place the gun on the wood and pull the trigger USING TWO HANDS! This is the technique suggested by the manufacturer. The problem with this technique is that if you apply insufficient pressure to the gun (USING ONE HAND) the safety is not engage so you don't shoot a nail. What usually happens - I just witnessed this a couple of weeks ago - is that not enough pressure is applied while pulling the trigger so you push harder and end up bumping the gun which shoots a nail - because you have the trigger pulled, but the nail shot was a surprise so it causes another bump (and is more apt to bounce because you're using just one hand). Because it is a machine and can operate faster than your reflexes - it shoots another nail. This happens before you can lift it off of the wood, or remove your finger from the trigger. That's the reason I keep the trigger pulled and bounce it. I know that after the bounce I've set a nail, and can remove my finger from the trigger. When I need to accurately set a nail I always use two hands, press hard and pull the trigger, and release quickly. Only pull the trigger when you know you're about to set a nail, and are poised above the workpiece.

SOURCE: Air leaks thru exaust on

Examine exhaust tube under valve for cracks and make sure that the tube seals correctly against body of the gun with rubber gasket. If tube is ok and has rubber gasket in place, check for correct cylinder movement. Press down cylinder with thumbs, the cylinder should return. If it stays down, pull it back up. If it is very hard to pull up, cylinder orings too tight or body of gun is warped. If it comes up with light to firm pull, go ahead and reinstall the head and test. If air leaks, try bumping the head of the gun (with air connected) against firm rubber to reset the cylinder against headvalve. If it still leaks, suspect that the cylinder is not moving up against the headvalve due to tight fit. Remove the cylinder and sand surfaces where orings contact to remove fine scratches with 400 grit paper. Also stretch the spring below the cylinder a bit to exert more pressue. Lube the cylinder with silicone paste lube. If you suspect warped body, remove all the orings from middle section the gun and insert the cylinder into body looking for out of round (with no orings the cylinder should just slide in to body of gun easily). Good luck