Carbon Buildup on Back of Intake Valves

When I removed the carburetor on my '07 Honda CRF250X, I took a peak inside the intake port and noticed quite a bit of carbon buildup on the back of both intake valves. Is this cause for concern or is this normal? I just got the bike and it appears to be in great shape for its age and the previous owner sounds like he took good care of it. I'm hoping the buildup was caused by oil vapor entering through the crankcase ventilation and not something serious. If I put the crank at TDC, is it okay to spray some cleaner in there and brush these deposits off or is that a bad idea? Here is a photo from someone else's intake valves--one of his was dirty and the other was clean, whereas both of mine are equally dirty: Attachment 44893 (http://www.doityourself.com/forum/attachments/motorcycles-snowmobiles-go-carts-motorized-bikes-atvs-electric-mobility-scooters-golf-carts/44893-carbon-buildup-back-intake-valves-valves.jpg)