My friend has a 2005 YFZ 450 with a White Bros Carbon Fiber Pro II pipe and pro flow air filter. I have just rejeted it because of a horrifying poping noise on the decel. I have a 178 main, 48 pilot, and the stock needle at the 5th position with the fuel screw 1 1/2 turns out. The plug looks perfect but still pops, so i put high temp silicon on the pipe to make sure there were no air leaks but still it pops. The carb is securely attached to both the engine and the air box boot. This is one of the worst popping noise i have ever heard and i cant seem to make it go away, no matter what i do it never changes it is always the same pop. Last year in July the top half of the engine was all redone because my friend (not very bright) put hot cams from a Yamaha dirt bike (i think it was a WRF 450 or something like that) in his quad and never checked valve clearance. While riding, one the the valve heads broke and was bouncing around inside the chamber, smashing everything, so it was all redone. I dont know if that would make a difference because i think they put i after market piston in. I checked the timing and it is right. Not really sure what to do next. Hope you have some ideas. Thanks!!