Engine Runs Rough

I have a LTR180. Sometimes it will not crank with the right stop peddle down. I take my foot off an it does crank. I push it down again an it cuts off. Occasionally it will stay running but not often. When it does crank it continues to run rough an miss while I'm mowing so much it will hardly pull the mower. Most times when I park it after mowing an I push the parking break peddle down the engine smoothes out like normal. Any ideas?

Engine Runs Rough