If your only on tank #4 then you're not through break in yet. Finish the break in then start to tune for performance. The carb comes from the factory very rich to ease the engine thru break-in then it's up to the owner to tune it for the best balance of performance and engine safety. By that I mean that it's possably to run a engine a bit rih so that it has a really good supply of lubricant and good performance or to tune it for all out performance with the side effect of a significantly shorter engine life span.

Anyway, watch these videos and you'll get an idea on tuning. They're for a HPI Savage but all small nitros tune the same way.
http://www.youtube.com/watch?v=oSmMzpZM_As
http://www.youtube.com/watch?v=BJFsJAxNoRg