Another tip that helped my bike with this same problem, make sure the idle adjustment screws are adjusted properly. Mine are about 3 1/4 turns out from closed. You'll probably need the D tool from Brent, but it's worth keeping in the tool kit. There are plenty of threads here about making these adjustments. I noticed on my bike at certain speeds in windy conditions the bike would bog/lag/etc...After adjusting the idle screws the problem is no longer evident. Hope this helps.
