1999 yamaha vmax 1200. backfire, poping, crackling at 4000rpm?

if i pull the plug wire off of #4 spark plug it stops doin it. or if i turn the air/fuel screw in all the way on the#4 carb instead of out 2.25 turns out like stock it will stop doin it also. so can anyone tell me wats goin on with my bike please? HELP? wat do i need to do to fix it right? thanks the other three carbs air/fuel screws are turnd out 2.25 like they should be. confused?