When I opened up the top of my carb to check the needle position, I noticed the inside surfaces were coated with a thin film of dust. I cleaned it out. The bike runs fine, but I wonder where the dust is getting in? I have about 2500 miles on the bike. This happening to anyone else? Is it a major concern? Maybe some dust is normal. I change my air filter regularly and put a bead of heavy grease around the seal. Thanks for any input.