The terms are a little confusing.
You should refer to the "main jet"
Or the "needle"
They are 2 different parts.
Don't call it a "main jet needle"... because that combines both terms and people can get confused.
The main jet controls top speed.
The needle controls mid range performance.
And changing them will only improve your performance if they are currently wrong.
You check this by doing a "plug chop" .
Read how to do that in the "How to fix your Moped" article under resources (above).