I was riding my '06 WR250F the other day. After a short break, I hit the button to start it, and it back fired. At the time I thought something hit my right leg, but did not think anything of it. After a few attempts I got the bike to fire, but it would not idle for more than a few seconds. It ran that way for the rest of the ride to the truck. When I came home and looked at the motor I noticed that the rubber vacuum cap was missing from one of the smog ports. It has a block-off kit. This is located on the right, rear corner of the head. I replaced the rubber cap but have not been able to test the bike because I took the carb off to clean it. Could the missing rubber cap cause the bike not to idle, or should I dig further into my carb (Pilot Jet) for the cause? Thanks for any information provided.