2007 CRF250R Jetting?

I would start by getting the pilot circuit dialed in. My 06 was really sensitive to weather conditions. A half turn can make the difference between the bike being easy to start and responsive or difficult to start and laggy. Mine liked a couple twists of throttle to prime it through the accelerator pump when cold. After years of tuning the bike I found that when it was set up properly you needed the choke/throttle to start it cold and hot start to start it if it stalled mid ride.

Some people run their exhaust valves on the tight side. They don't tend to tighten up nearly as often as the intakes. If they're below minimum spec go ahead and shim them. Be sure to check the valves every few hours for a little while until you know they're staying put.

Accelerator pump tuning can improve throttle response. I tried a few different setups. The o-ring or wire mod, shaved diaphragm rivet and a 45 (I believe) leak jet worked best for me. The timing is also critical and should be set to just miss the slide as it rises.