yz250f help

i have a 2004 yz250f. I am looking for some advice. i ran the bike all last year and it never gave me any problems. I put the bike away for the winter and started it up a few weeks ago and it still ran just fine. After i ran it a few times i noticed that i was starting to get some back fire on decel. I checked valve clearance and intake is .001" over spec, and exhaust is right at the lower spec limit. I am wondering if i maybe sucked something into the carb?

any advice would be great

thanks
grensjos

thanks for the reply, i think that i may have solved the problem. The gas that i filled the tank with last was about 6 months old and had broken down and must not have enough octane. Stupid mistake on my part!

thanks
grensjos