Hello out there. I'm new to this forum and looking for a little help. I have read a bunch of the posts and it looks like there is a lot of experience here. We just bought a 2005 Trx400ex and I am having a problem apparently with the air box. It ran pretty good when we got it home and then about three days later it acted like it was loading up and trying to flood at higher rpms. Breaking up and sputtering. Low r's it was okay. I changed the plug and it still did the same thing. I discovered that if I ran it with the lid off the air cleaner box and the air cleaner disconnected, the thing runs like a raped ape. I have checked to make sure there is no blockage in the intake system and the air cleaner looks good. Could this be a vacuum problem or is there something about these that I need to look at instead? Thank you for any words of wisdom you might have to share.