Hi, I have an 04 Bonneville that will sputter and back fire at start and until warmed up. My first guess was bad gas and tried some different gas treatments. Next I tried new spark plugs. Yesterday I got my bike back from the shop with a carb clean. This morning again started with sputtering and a couple of back fires. Had to ride with choke out for a few minutes or else when I slow for a stop and then give some throttle it will sputter and sometimes backfire. Once warm the bike rides great...usually within 5 to 10 minutes depending on how cold it is outside. What should I check/do next? Thanks for any advice.