So I got my Snapper up and running again after another carburetor and fuel filter change. It's got a 286707 Briggs 12.5HP I/C and originally had the LMT carburetor. It runs pretty decent and you can mow the whole yard without cutting off. Start up pretty easy. However you can still hear while driving around or mowing the engine searching for a steady RPM. It fluctuates up and down every couple seconds. Not enough to cause any issues such as cutting off. It's just enough to know there is still something wrong. I've changed the carburetor a few times even back to the original Briggs LMT. It doesn't matter what carb is on there it still does it. I got the mixture right on, the idle at 1200RPM and high speed idle match the engine at 3000-3100. Did a governor adjustment but it was right on too, I think it was 1750RPM. I rechecked the ignition coil gap, checked the flywheel key. Adjusted the throttle lever control. I'm just wondering what else could cause this issue. I notice there's a guy on youtube that did a video that was having the same problem and as trying to find solutions. Could it be there is a burnt exhaust valve or cam problem? It doesn't smoke though. I know there governor bracket rack and pinion control arm appears to have surface rust but it moves freely. Anything else I could check?