I run Marvel Mystery Oil in every tank of fuel, about 1/2-3/4 of an ounce. Many say snake oil doesn't work but I have had good luck with it on my bikes, lawnmowers and all small engines. The last bike I bought, a Honda Shadow Spirit 1100, I was told needed a carb overhaul. I test rode it before I bought it. The bike popped and surged a little like it needed a carb overhaul. I paid the guy and left it at his shop until I could come back and pick it up. I brought gas with MMO in it, rode it off, got it inspected and title changed in the same day. That was a miracle. I never did anything to the carbs and now it runs perfectly. I have had it over a year now. Back to your TW. Have you done a compression test? Have you tried another plug? I have had plugs cause backfiring. I have had bad valves cause backfiring. Have you checked your timing chain tensioner to see if it's adjusted to spec? If it is still your carb, there is a hole in the throat of the carb that causes issues if it becomes clogged. I think it causes more midrange issues though. If it is mainly in your idle, add Berrymans Chemtool B12, Seafoam or MMO and go ride it in places where you can keep going. Maybe it will blow through after some hard riding. Another thing to check is fire it up at night and mist around the spark plug wire with a spray bottle of water and see if you're losing any spark. It will be great when you get this thing up and running like it should. Good luck.