Juergen,

How did you break your engine in?
Read the break-in threads in the forum and make sure you followed them. The 46FX is an ABN tapered bore engine.

The correct adjustment of the high speed needle is:
With the plane nose-up, close the needle until maximum RPM is reached (where leaning it further causes a loss of RPM), from there open (richen) by 2-3 clicks. The Dazzler is a fun-fly, with not too much unloading as flight speed increases.

The sole purpose of the high speed fuel needle, is to control the amount of fuel the engine gets, at 80%-100% throttle.

Once this needle is adjusted, it has no effect whatsoever, on the mixture the engine is getting, from 0% to 75% throttle.

Since in both letters you did not bother to mention the idle mixture needle, I conclude that you did not bother to touch it either. Maybe you were not told where it is.

The idle needle is the small screw inside the throttle barrel, on the same side as the throttle arm. In all OS engines I saw, the Idle mixture was adjusted too rich to begin with.
Since despite its name, this needle has control of the mixture at up to 75% throttle, you will not get what you bargained for, until after you have adjusted it correctly.

This needle is very close to the spinning prop, so utmost care must be taken, so as not to get your fingers and your prop into a conflict, over a given volume of air.
It may not be a bad idea to shut the engine down, make the adjustment and restart it to do the check.
Also, when you push the needle with a screwdriver to turn it, it moves enough to shut the engine down, or to affect its running.

Close the idle needle 1/8-1/4 of a turn, with a small screwdriver, gradually open the throttle to full , run the engine at high RPM for a few seconds and close the throttle to about 1mm open.
Allow the engine to idle and listen to it.

If RPM declines gradually, it is still too rich. Repeat the last paragraph until the engine does not sag, then you are in the ballpark. If, on the other hand, RPM increases gradually, you are a bit too lean.

After you finish adjusting, allow the engine to hold the idle for at least 30 seconds, after which you open the throttle rapidly. If the engine goes to full speed immediately, you're done.

If it stutters and spits fuel while speeding up, you're still rich. Close the idle needle a bit more and retry.

If it cuts and dies, or cuts and eventually goes to full speed after a delay, you are too lean, open the idle needle a bit and retry.

Get it right before you try flying again.

Sincerely,