Have you checked the fuel tank vent line for restrictions? Try running it with filler cap loose or off completely. If it runs better check the vent hose for mud, kinks or being melted shut by the engine/exhaust heat. Mine melted shut against the exhaust pipe and would stall under full acceleration. Buddy
I know the "VOICES" aren't real but they have some great ideas.
1999 Sport 400 2x4
Complete rebuild w/Wiseco piston by Todd Kerby, Comet clutch, Swamplites front & rear, 03 Predator Rear Hubs,
ITP Pro Baja Wheels (4x156 front & rear), DG Front Bumper, Fuj Rear Grab Bars and RZR Belt