In Reply to: Exhaust Soft Pop posted by Max on October 15, 2018 at 20:41:34:
I assume this is at slow idle less than 500 RPM. At a fast idle, the tractor is already running on main mixture, so the idle air mix adjustment screw does nothing. Random pop at idle is usually slightly lean, try pulling he choke slowly out. If a little choke makes the problem go away, that confirms engine running too lean. Adjust small idle air mix screw in and see if that fixes it. If engine is idling at slow idle and turning mixture screw in does nothing, the engine may be sucking air past a loose throttle shaft, other leak, or the carb idle fuel passage is restricted or blocked. The idle mixture screw controls idle air, so cranking that screw in as far as it will go is as rich as it will go. If pulling choke a little still clears up intermittent popping, spraying wd-40 around likely leaks may identify the problem, or the idle fuel passage needs to be cleared or maybe enlarged. Idle fuel jet may be too small, but problem with idle fuel flow is usually restriction in the fuel passage.
If pulling the choke slowly makes the problem worse, it's running too rich. Turn idle air mix screw out a bit. If turning the idle air screw all the way out does nothing, the engine is most likely not running at idle, it's running on the main mixture. Without a tach to gauge engine rpm many people don't realize how much slower a 450-500 rpm idle is. Many cars and trucks normally idle around twice that.