JD LT 160 16HP Kohler suddenly runs poorly
I have a 2003 John Deere LT 160 with a single cylinder 16HP Kohler. It was mowing fine on Saturday. On Sunday, when I started it, it backfired several times, finally started, and it now runs very poorly. With the throttle at full, it doesn't develop anywhere near full rpm, actually seems closer to idle rpm. And seems very loud at that. As I slowly close the throttle, RPMs actually pick up a little, but then decrease as throttle is closed further. If throttle closed to idle, engine will die. If throttle is advanced into choke range, engine bogs and dies. Any load on engine (e.g. engaging mower clutch) will pretty much kill it.
Fuel pump is delivering fuel. Pulled the plug, and it was dark brown, with a little carbon on it. I cleaned it up and gapped it to 0.040", per the book.
Any ideas?