hey guys i know im a newbie on here but we play with a few crf250s at our little shop out here in aus, this info might be of some use.
My current bike is a 2010 250f with close to 80 hrs on it, with most of these hours coming on an mx track and a bit of desert style riding, I havent had to adjust valves once. However on my bikes before efi we were adjusting valves every 40hrs or so.
I am not the only person who has found this with most people on efi crfs around our area getting close to 100hrs before valves even look like moving (unless its some clown who can't change air filters).
The only reason we could figure for this change was the new fuel filter which had been added with efi. With this filter becoming bloked to the point where the bikes wont run at around 50hrs we figured that it could be the dirt moving through fuel which was causing valve wear on the older crfs.
Customers never believe us that they have dirty fuel until they go home an
take the filters out. I even got two new fast fuel drums at the start of the year and still have the same issue. The fact is we just have crappy fuel out here in Aus might be a problem where you are to.