Went on a mountain trail ride last weekend and it kept backfiring, this was the first time it has done this. There are no engine or exhaust or fuel delivery mods done. Any ideas would be helpful thanks

 

It probably only happens when you let off the gas, right? Air is getting sucked into the exhaust (you have a small leak) and that's the problem. I have 2010 Brute with the same thing happening. No matter how I move the clamp and tighten it, I can't get it to seal. My next step is to buy some hight temp gasket material and try to spread a little bit of it at the joint between the pipe for the front cylinder and the muffler.

Use a bottle of soapy water and spray the exhaust while the machine is running. You will see bubbles coming from the spot that it is leaking.