...Fein,


This may be the cause of your problems.
Residues of silicon oils tend to settle on the glow plug element and create a scale-like appearance.

This masks some of the element's platinum from the fuel's methanol, which prevents it from catalytically reacting with it, to keep it hot. This is the whole basis of glow ignition.


...Driver,


The carburettor that ST engines come with, does offer the possibility to fine-tune the mid-range, by releasing the screws that hold the spray-bar assembly and rotating it slightly.

In most fuel metering carburettors, the low-speed needle (/disk/other) controls the mixture strength, from idle to about 75% throttle. In ST, the spray-bar adds this fine adjustment possibility, for a better tune.