*NEED HELP* 04 is running terrible

[BlaineKaiser450]

my 2004 450r is running terrible/hardly running. The only motor mods that i have are Pipe/jetted and stuff and a brand new (3 hours on it) CP 12:1 piston. Last weekend i rode at a VERY dusty track and towrds the end of the ride my quad started to pop on deceleration which was funny because i had it jetted perfect. I figured that it was the filter being dirty so i cleaned it and just started it up again. That didnt make a difference. The quad pops really badly and pretty much acts like it is lean but it is jetted perfectly. Im also worried about the oil because it was almost the milky color that you get when a head gasket goes. So far ive cleaned the jet, changed the oil, cleaned the filter, and messed with the Air/Fuel screw and nothing has changed. Im thinking that MAYBE the head gasket is starting to go. Can anyone help me here? thanks in advance

[Butter]

I think you already answered yourself. Anti-Freeze getting into the oil making it milky, and anytime you get off the gas, its sucking air into the head, thus making it seem lean. Did you put a new head gasket in when you put the piston in?

[mooseracerX]

I don't know about the 450's but on the 400ex's the carbs, and carb tube has a tendency to fall to get loose and cause it to suck too much air and run like you described.

[d3ktrix]

Sounds like the head gasket.

Check for exhaust leaks too at the header.