Sometimes the CIS fuel system is prone to backfires. This can cause a small explosion within the CIS airbox. Without some type of pressure relief valve, this explosion can blow apart the entire airbox. Replacement airboxes are several hundreds of dollars. The work-around is to install a pop-off pressure relief valve in your CIS box. The process is quite easy, and it's very cheap insurance against costly backfires. Click here to view the Pop-Off valve tech article. Or click here to download installation instructions.