Limit leingth of body text of event when promoted to front page?

Hi.

I'm new to Drupal but comfortable with php.

Currently testing Drupal and the event module along with event manager and event manager block.
I have made simple modifications to, for example, put the start and end dates on the same line, and stop the timezone section from being shown altogether.

I have a number of events where the body of the event can be rather long and when a new event is promoted to the front page on publishing I would like to limit the body text to around 20 words. Try as I might, I simply cannot find a way of doing this. I only want it to limit the body text of events and not of other items posted.
Any pointers on how to achieve this please?

Ken.