Asmund,


This information is correct, but also very partial.

It is important to verify that the engine can repeatedly recover to that maximum, measured RPM, after running at part throttle.

Finding the so-called 'peak' is done while also tweaking the needle; not only extending and retracting the pipe.
Often, setting the pipe this way result in having to pinch the fuel line momentarily, for the engine to get back on-the-pipe.
It cannot reach the base-line RPM of the system at its richer setting (to provide enough fuel for on-the-pipe operation).

This obviously cannot be done in flight, so a slightly greater tuned length is needed, for the engine to get on-the-pipe, on its own, with the main needle at a safe, not-too-lean setting.
A greater pipe length is needed, to be tuned for the lower RPM, the engine is capable of reaching on its own.

So you would want set the pipe to a length that would provide a slightly lower-than-peak RPM.

Too short a pipe can burn up your engine, if it only gets on-the-pipe when flight speed unloads the prop, resulting in too lean a mixture.