Unrelated to my last problem with the coils, I think....
I was having a problem with the engine sputtering under heavy load and I finally ended up replacing the coils and it once again ran perfect. It just so happens that only on my second time mowing since the coils were replaced, I hit a large rock while backing up (the rear of the deck caught it and pulled it up). The rock is large....maybe 2 feet long and 4 inches thick. It nearly stopped the engine while it was running at full speed with the blades engaged. Only a few seconds passed before I had the chance to turn off the blades. Once I turned off the blades and lowered the engine speed to idle, I noticed that it was sputtering, at idle. If I sped up the engine speed it seemed to go away. I continued mowing and it was strong and smooth from the best I could tell from my seat. When I was done mowing and I lowered the engine speed I noticed it was surging and sputtering again. I can only assume something happened mechanically to the engine when I hit that rock with the engine speed at full throttle and the blades engaged. Does that seem possible or is it just a coincidence? As you can see, when I pull the right side spark plug wire off at idle, it doesn't change anything at all, but it should be very noticeable when the plug wire is pulled off. If I pull off the LEFT side plug wire, the engine nearly dies. If I speed up the engine speed it's better, but it doesn't sound right. Any ideas? Valve problem due to hitting that rock??? Since the suspect side is on the side where the oil fill plug is, I reached my finger in to see if the valves were moving when the engine was turned over with a socked on the rear shaft and each valve does move but I can't tell too much since all I'm really doing is feeling if they're moving. I don't know how much they're moving and if it's the correct amount and correct time. This is very frustrating. If something happened to the engine after I spent all that time getting the coil problem fixed, I'm going to be really depressed :-( I don't know...maybe something odd happened with the right side coil like it's not in the position it should be in or something after that jolt from hitting the rock. I just don't know. Both plugs look the same visually and I even swapped them (they're both new too, after the coil replacement).
Here's the video. What do you think???