Misfire with Craftsman YT-4000 Briggs-Stratton Platinum Series 24 hp engine

I have a Briggs-Stratton Platinum Series 24 hp V-twin engine that is misfiring when sitting and running full throttle without mower deck engaged. When at half throttle, sitting and no load engine runs fine, but if I put tractor in gear and move it will occasionally misfire. When at low idle, no load and in gear moving there is no misfire. Also noted that when I engage mower deck at full throttle the misfire stops, however after mowing for about a half hour to an hour engine will misfire occasionally even with the mower deck is engaged. Only previous issue was that the clamp that held the throttle cable in position to the engine worked it's way loose six mowing times back. At that time I reset as was directed and had no throttle issues or misfires. Currently I have removed cowling and top shroud so I could look at the plug wires and visually inspect the magnetos and operation of carburetor linkages. Also checked flywheel key, it looks fine. As well, I also drained gas and repurchased gas from another filling station/ same results. At the moment perplexed and lacking specific test equipment beyond hand tools, patience and open to suggestions from others.

If it would require air or fuel mixture adjustments, I have no clue as to their location as I'm sitting here looking at the carb.

Engine has 105 hours on it and I just had completed the scheduled 100 hour service maintenance on it. Changed oil, oil filter, fuel filter, air filter, spark plugs and am using fresh fuel.

Any thoughts and/or suggestions from other members would be greatly appreciated, thank you............. NotSoHandyman

Was engine running fine before replacing spark plugs, filters, etc? If it was running fine prior to working on engine, make sure you have correct B&S spark plugs & gap is correct. If you do not have engine manual just enter model & trim numbers from engine data plate for your operators manual & parts list.

https://www.briggsandstratton.com/us/en/support/manuals/engine

The interval you are on is about the time my Intek started misbehaving from new. Check the valve clearances and look at the exhaust valve guides to make sure they haven't begun to move in the head. Also have you hit anything that could have bent or sheared the flywheel key, throwing off the timing? Use the search function to see a pushed guide.