If your engine's modified even a little, then the fuelling will be out, at least at some point in the rev range. The more the engine is modified then the more the standard needle profile will be out.
Profiling needles is not difficult and can be done with basic tools, saying that it's not a matter of guesswork and need to be done accuratley.
Fitting an air/fuel gauge and Lambda sensor will allow you to monitor any changes made to fuelling and monitor at which points the engine is running rich or lean. See here for fitting an air/fuel gauge & lambda sensor.

I use a set of digital verniers & measure the needle at 5mm increments from the shoulder of the needle.

More coming soon.

It's useful to get a piece of paper & draw small lines every 5mm, so you can lay the needle next to it & measure at each point. As long as you line it up properly each time you'll know you're measuring the correct point.