pcr pdt amplification - (Mar/04/2009 )

hey guys am facing problem with 16s PCR amplification. the samples i am working with, are insect gut DNA samples. even though the DNA yield is good from the gut tissue, i am unable to amplify the 16s populn. of a few samples. while some samples show a very light band that does not increase in intensity even if the cycles are increased upto 40. it would be great if you guys could help me in troubleshooting this becaause right now am stuck at this basic level and cant proceed beyond it.

Tell us:
primers being used
PCR reaction setup (enzyme, amounts, buffers, dNTPs)
Amount of template being used
Methods of template purification
Cycling conditions