I bought the bike for my kids a few weeks ago. when its cold its really sluggish and pops back through the air intake. I have already thoroughly cleaned the carb on it 2 times. every thing in there looks good. It seems to be a lot worse when it is cold outside. Once the bike warms up and has been running for about 10-15 min it runs alot better still a little issue but nothing like when it is cold. The carb on the bike is a walbro and has a built in fuel filter which I have cleaned as well. Could this be a valve issue or do you guys think its fueling related? It seems to me like its lean. I noticed that some one had taped off part of the air inlet on the air box. I removed the tape and it ran even worse. The quad was manufactured in 2006.

Any help would be very much appreciated. I have found tons of info on the 2 stroke version but nothing for the 4 strokes. I havent found any info as far as factory jetting or cab parts.