Get a flying instructor to show you how to burn the dirt off the plugs !!!!!! ??????????? god help us !!!!!!!!!.
You had better make sure its an instructor who is very long in the tooth ! most of the young ones seem not to have the first idea about how an engine should be used.
If you think I,m being harsh just take a look at some of the technical posts that we have seen on this forum over the last few weeks , a lot of this is the result of there teaching ( or lack of it ).
Perhaps a visit to the engineers would cast a bit more light on the subject and wile you are in the hangar no doubt they can show you a few of the cracked cylinders that they have removed due to inproper leaning of the mixture.