Outdoor Power Equipment and Small Engines - Problem with Kohler engine

I have a Cub cadet GT-1554 trctor with a Kohler SV-740S engine. It ran fine for first 13 months then all of sudden does not run right anymore. It ran fine 1 day then the next it runs very irregular. I have put in new plugs, tested the coils, put in a new black box, and check the fuel system no change. Does anybody have any ideas what it might be???

What is it doing? How did you check the fuel system?

What black box? Did you coincidently make any repairs or otherwise service/maintain the engine at the time, or just prior to, you developed the problem? Oil change? Air filter(s) replacement? Fuel filter?

I had just used it the day before to cut grass, came out the following day and started it. Instead of running smoothly, it ran erractically (missing at random). I got the service manual from the Kohler site, and went thru their tests. This engine has what they call Smart-Spark variable timing black box.

Thats why after testing the coils, putting in new plugs, and checking fuel, I thought the black box would be it. Wrong!!

I also drained and refilled the gas tank. There has been no change.

You mentioned twice checking the fuel system. What do you mean? Did you clean the carburetor? How does the air filter look? Have you run it without the air filter? I've never seen a smart spark (SAM) go bad. I guess you can't return it either being an electrical part. Too bad, those things run 110 bucks or so if I recall correctly.