Now not about the diesel manipulations, but about something that occurs more often with classics: Nadieselen
When the ignition is switched off, the engine runs - messy - for a few more turns.
The disadvantages can sometimes be solved or reduced by (after checking for proper operation and) setting the ignition on time and / or regulating a lower idle speed and / or a leaner fuel / air mixture.
If that doesn't work enough, there are a few tricks. If the engine is running at idle speed, depress the clutch deeply. You often notice a limited fall in speed. If you then switch off the ignition, the disadvantages will disappear in almost all cases.
Stripping through the bucket in the highest gear, the brake and the clutch is working is sure. But if that is the approach, then we would still look further
Do not forget to switch off the ignition after wiping off