Can be many things;

1) How old is your fuel? Was it sealed with the original cap? If not - did the bottle cave in on a cool morning? no- chuck it and get a new jug. Yes, May still be dead.
Reset the needles to factory spec and get a tankful from an different source. See if it helps.
Reason: Fuel absorbs water from the air and it won't burn well.
This cured mine more than once.

2) back flush the fuel system including the needle valves.
Or do a complete teardown on the carb and clean it out.
Then reset to factory recommended on both needles and start over. Make sure you have fresh fuel, see #1
Reason: crud in a needle is impossible to adjust.
This has also helped me a couple times.

Ramjet - fly Hard!