What temperature is required to burn pencil lead graphite?
You have two problems.  
1.) pencil lead graphite is actually a graphite-clay composite. 
2.) carbon does not sustain burning easily unless it is held at very high temperatures.

Pencil lead will not burn effectively for the first reason as clay is non-combustible and smothers any fire load. If you did have pure graphite to burn, a simple flame wouldn't be hot enough to combust it.  You need to sustain temperatures of around $1000\mathrm{-}2000~^\circ\mathrm{C}$ in order for pure carbon to burn.