Problems with PCR following bisulfite treatment - (Aug/30/2006 )
try using a restriction restriction enzyme before you convert your DNA. It should improve the specificity of your PCR.
Further to Bram's comments,
you could also shear your DNA by passing it through a 19G syringe needle or sonicating it. I tend to find this easier if you are intending to analyse many loci within the genome for methylation.