Not tighten it down more than usual.. just tighten it down properly.. hee hee.. often time people set it too loose..

You really should set the diff once you got the wheel/tires on.. when try to set it during the build, it is harder to gauge..

(Unless the instruction is the type that says to tighten it all the way and then back out a 1/4 turns, etc.) That you can do... but in most Tamiya build, it does not give that kind of instruction..

Good luck!