Well, if you are pretty sure it is neither flooded nor too lean to start, then the ignition could be suspect. If you are using a 4.8 volt battery pack, try a 6 volt pack. I have had marginal ignition systems work when trying that trick. I have had ignitions that would show a spark when checked, but not want to start the engine until using 6 volts. Bill from CH told me about the 6 volt trick....

If that Turnigy came with the "blue box" ignition, they are known for failures.

AV8TOR