Hello I have a 2002 400ex and it started to loose power one day but it still drove fine and then the next day it started to make a like poof noise once and a while and then I checked stuff and it looked fine so I went riding and it started to bog down and stall out offten when I give it some gas to go fast I changed the spark plug and it still dos it when it runs now you and some more info if it helps it back fires often and when I pull in the clutch it doesn't idle but then when it's sitting it i runs for a little then it goes to a really low idle back to high ect. And I can hear the carb squirting when starting it