I'd like to note that I've spent 15 years working on engines from minor repairs to full rebuilds (bought an 09 Subaru legacy from a kid that drove it without oil, rebuild and now daily that vehicle) so there is a reasonable amount of experience (so I like to think). I have a 2016 Exmark Turf Tracer 60" X Series I recently acquired. Kohler ECV650-3017 EFI. Worked great for the first few cuts, maybe 5 hours. In general, pretty good shape. About 1170 hours on the unit. Engine oil is new and full. Hydraulic oil is in the proper range (not that this applies right now). I'm terrible at explanations (too much info usually) so TLDR at the end. One day I started it and we were running one 1 cylinder (the operator's left cylinder was cold). Let it warm up for a few minutes, the cylinder would kick on and we'd have full power. I cut the yard and moved on. Next time, I was on 1 cylinder again (left cylinder cold). It looked like my left cylinder had no spark, so I got new Kohler coils. This fixed it for a cut or two. Then back to 1 cylinder (left cylinder cold). I took off the new coil, and installed the new "good" coil (from the right cylinder). Worked great. Then we are back to the same old BS after a cut or two. Left cylinder cold. Thought I burned up the left coil, so I did some homework. I bought a new Kohler regulator/ rectifier based on the reading I've done. ANYWAYS, new R/R didn't help. I've got solid spark on the left though. While the engine was running on 1 cylinder, I sprayed the airbox with engine starting fluid and there was no difference. This tells me fuel is not an issue. The strong spark I saw tells me the spark is not an issue. I tested all the coils, and they have the same resistance values for primary and secondary coils. There is continuity throughout the block for ground (sounds silly, but I know funky ground connections cause real funky gremlins). The ground wire from block to battery is solid. New Sparkplugs, too. TL;DR Coils test as good. New plugs. New Regulator/ rectifier. Engine will run on 1 cylinder randomly, yet is somewhat consistent (engine runs steady on 2 cylinders or 1 cylinder). When running on 1 cylinder, starter fluid sprayed into the airbox makes no difference. Confused to death. Help?