I just put a turbine core silencer FMF on my nephews Blaster it ran great, then we changed the air filter to a uni filter and put 6 vent plugs in the filter box, (I did not re-jet or put that Fatty pipe on yet)now after it starts the exhaust is popping and it will not stay idle, I was thinking to turn the mix screw out a half of turn. Need help I know that works on my 400ex when I did my mods. Need help with the 2 stroke. Thanks I will be re-jetting to 260 once the fatty is on, thoughts on jetting will help to. It is a 2000 Blaster
400ex 2002
E-series
ac racing nerfs& bumper
K&N jet Kit & filter

 

It sounds like it is just back firing. Change your jets and see if it still does it. If it isn't back firing than I have no idea.

 

IF THERE ARE NO LEAKS IN THE EXHAUST/INTAKE/MANIFOLDS/ VACUME LINES. TRY TURNING YOUR AIR OUT 1/2 TURN.