if you have no spark
check for faulty plug 1st, then pull kill wire off at kill switch, then check for grounding ht lead ,
then pull kill wire off at armature , if still no spark most likley faulty ignition armature
i suspect the part number you need if its type 1 is 15662639130
replace it and set air gap and reassemble and test
here is web site for parts
http://www.ereplacementparts.com/echo-cs3400-type-chainsaw-parts-c-35043_35970_36021.html
or you could try
www.partstree.com , go to echo saws , then find your model
cheers hope it helps
pauly 46