Control teaser lenght when using process hook

I have created a custom tags module where I use the process hook function ( _reptag_[my module name]_process ) to fetch a large page from outside my site and include it into a node.

The problem is that the teaser for the node shows the whole fetched page (a very large one), and does not obey the teaser word count limit.

Is there any way to get around this?

Regards
// Samuel Lampa