JD L130 with a Kohler CV23S 77769, about 11 years old.
I did maintenance work on it about a month ago. Owner mentioned that the engine dies when pulling the (electric) PTO. I found that it would not kill the engine if it was engaged at about 1/2 throttle (which is easier on the clutch, anyway). Then I found that the air filter was not installed correctly, and dirt had been entering the engine. The owner told me he takes it out occasionally to blow it out. I told him he was not installing it correctly, plus blowing out the element wasn't as good as a new filter because the pores clog. I told him his engine had most likely incurred excessive wear as a result.
Both spark plugs had good color, no dead cylinder.
Anyway, he called me over the weekend to tell me it's dying again when he pulls the PTO. I haven't returned his call yet, but I figure I'll check spark on both cylinders to be sure, and do leak down and compression tests.
Any other reasons it would die? I don't feel it's in the wiring, as it would stay running when pulled at 1/2 throttle.
EDIT: I just spoke with him. I told what I mentioned above, and said it's certainly possible that a safety switch is acting up since I was there working on it, and to make sure the mandrels and idler pullys are free. He said nothing is wrapped around the blades.