Yeah, Clutz, you should really pay your mechanic better

Jokes aside. Is the Spit the only plane this is happening in? Only primary guns or only secondary, or both? If you hold trigger and the gun sounds funny, does the ammo count go down? Do the "invisible/non-existent" bullets do damage (best checked with bulls-eye
.target ### command)? Does it only happen when you hit fire button on your Joystick or as well if you use keyboard to fire?
Another thing you can try: Backup your
Settings folder. Then delete it. Upon restarting the game will create a new one with Default settings. Does the problem persist then?
Also post a dxdiag output. Maybe the "missing tracers/gun flashes" are a vid card/driver related thing.