Tractor has 1,400 hrs on it. It does smoke a little a startup. It started up like normal/fine this morning. I pulled it up on my trailer (to go mow a friends place) and shut it off. Get to the friends place and start the tractor to back it off the trailer. It was slightly sluggish starting but started up. But I could tell the engine was running different and it sounds like there is a popping noise coming out of the muffler. Engine RPM's dropped to the point that trying to mow was basically impossible. I suspect it's only running on one cylinder now. With the engine running I placed a gloved hand on each valve cover. I could feel some warmth through the glove on the left cover but not the right cover. Even with my bare hand I could not feel any warmth on the right valve cover. So I took the plug out on that side and checked for spark as I turned the engine over. I could see spark. So where does that leave me ? I'm not a mechanic but the popping sound coming through the muffler makes me think it's the valve issue on that side. Suggestions ?