After changing my carb to the TRX450 carb my DS has started to pop and backfire when I let off the gas and if I down shift to slow down it gets worse. It doesn't do it if I pull the clutch in right away. I'm still getting the carb tuned but does anyone have any advice on what the problem might be. I think the muffler needs repacking because it's getting louder under normal throttle.

 

The pilot (idle ) circuit is too lean. Could be an air leak, or pilot jet too small or mixture screw too lean.
Is the air cut off valve hooked up or blocked off? If you blocked it off, that will make the back fire happen.

 

I'm not sure what you mean by air cut off valve. I would say it's probably not hooked up. But could you describe it to me in more detail?
Thanks for the help.

 

If you look at a honda parts finder, youll see the cut off valve. A vacumn line needs to be hooked up to it. The purpose of the cut off valve to to stop the back fire on decel...it prevents a leaning out of the idle circuit at high rpm, closed throttle conditions.

 

try a bigger pilot then adjust your A/F screw from there, good luck.