Pretty much I think it's a fuel problem some where you hardly touch the throttle and it Revs right up but as soon as you let go it shuts down fast. I also believe that's why it's kinda hard start as well

 

It also sat for 4 years prior to me getting it so it need some cleaning up and tlc

 

Clean out the carb and throw a carb kit on it.New Polaris Xplorer 400 1997-2002 CARBURETOR Carb Rebuild Kit Repair US | eBay Just zip tie the upper carb vent tubes to the choke or throttle cable and let the ends terminate under the tank. Run the bowl drain/overflow tube past the bash plate to keep fuel off the engine in case it ever leaks. On these old model always turn the fuel valve off after use.