Matching data in two tables

This is probably pretty rudimentary but I'm doing an Update Query in 2007 and
I am having an issue with my criteria.

I have two tables:
tbl_1 contains a column with a serial number (14,000 rows) .
tbl_2 contains a column with user description information that includes the
serial numbers I want to match. (45,000 rows)

tbl_1 field: 673567
tbl_2 field: FTN 673567 333, Doe John, W, X,

Here is my query in SQL:
UPDATE tbl_2, tbl_1
SET tbl_2.[Compare Match] = "Match"
WHERE (((tbl_2.Descriptor) Like '*' & [tbl_1]![Serial Number] & '*'));

I actually get this query to work with smaller data tables, but there seems
to be a conflict with the size of my two tables and the criteria I'm using to
do the match (200 rows against 14,000). Any ideas. This really should be
jumping out at me but it is not. Thanks.