Limit size of RSS feedtext

[Ghostt]

Database error in vBulletin 3.8.4:

Invalid SQL:

		REPLACE INTO vbexternalcache
			(cachehash, dateline, text, headers, forumid)
		VALUES
			(


...........

MySQL Error   : Got a packet bigger than 'max_allowed_packet' bytes
Error Number  : 1153
Script:    /external.php?type=RSS2

I am getting this error i think because there come to mutch BIG Theards to rss .
for example first 200 characters.

How can i limit the size of the text in rss?
if it isnt possible we need urgent a mod to find!