[mrchris1979]

It is coming from the exhaust. The bottle pressure has been below 900psi so I'm guessing the fuel mix might be too rich. Causing the backfire. I have sprayed at about 800psi a few times and never had the problem. I don't keep the bottle heated all the time cause the NX heater requires the bottle to be open to regulate the pressure. It's warmer outside now so the bottle stays at about 850. I guess now I do have to keep the pressure at 950 to prevent this. Do you know of other problems that might cause this besides the rich fuel mix ? Down sizing the fuel jet seems risky, but if you had experience with downsizing the fuel jet, I'll try it out.