I have a Polaris Ranger 2005 500 cc. Starts and idles great. under slow increase on throttle response is ok to marginal. Push foot feed down quickly and engine bogs out and dies. New Valves, cam chain and sprockets. Cam Lobes are fine. Swapped out carb for a new aftermarket and no better. Mechanic has been chasing fuel system issues but we are both getting stymied. New plugs. Air box is wide open. Engine ran prior to valve replacement but has sat for 2 years or better. Time to figure this out so am looking for advice. Could this be an electrical problem. Timing is on the money. thanks for the help.

 

Just a thought here, most machines are designed to be run with airbox and filter in place or a lean condition can occur. When you say airbox is wide open, are you meaning everything is in place?
Next check plug color, should be coffe brown or slightly lighter. Gray to white is lean, dark brown to black is overly rich. Hope this helps...