Mimi,

We have a similar setup in our lab (GFL 1086 interfaced to a Delta
Plus)and have had some of these problems in the past.  You may want to
check your hoko sticks or hoko beads for the HD analysis.  Are they new? 
If not, what types of samples were analyzed in the past using those same
sticks?

You will also want to check for consistency in temperature throughout the
bath.  It may be cooler or warmer at one end causing the problems you are
seeing.  I am not sure how to avoid this problem except to circulate the
water through the system at a constant temperature.

You may also want to recheck your equilibration flasks for leaks (even
small ones).

I hope this helps.

Art
-- 
Art Kasson
Cornell Isotope Laboratory
Dept Ecology and Evolutionary Biology
E440 Corson Hall
Tower Road
Ithaca NY 14853 USA
Phone: 607.254.1382
Fax: 607.255.8088
COIL website
http://www.cobsil.com
Isogeochem website
http://www.isogeochem.com