Hello, i have a polaris magnum 425, 96', and i have engine troubles.. It runs ok at idle and mid range, but will start to rev to top end and then die out.. The plug is white which means lean but when i take the air box off it runs fine ! I dont understand it.. I went throught the carb twice and it has stock jets, cleaned all and still same thing.. Any help would be appreciated.. Tried different fuel pump, no dice..