Mine has done it with old and new regulators. More so when cold. Might be able to clean it up with a good PC tune, otherwise bliping it is the problem
I know, it fun and sounds neat but bike needs to be warm or it'll choke.
If it has been happening on a warm bike it very well could be the FPR.
2001 #62. Ohlins rear/valves, Micron high mount, HyperPro damper, SharkSkinz, Tyga billet triple clamp, Tyga Carbon Fiber fender and hugger, Ti bolt/custom subframe/alien motion 8 cell diet, 15/41 520, COP conv. PCIII, Venhill lines, modified air box, turn signals in headlights...<deep breath> ZG Touring windscreen, Tech G rear sets, CRF450 rear master w/HRC cover, Tokico 6 pots w/V-pads, CRG Bar end mirrors, PSR Shorty levers-use only clutch, wanna-be basic racer paint, Roman Gold PC wheels