Husqvarna 125B won't start.

Check for actual SPARK at the plug, grounded to the block.
 
Check compression (should be at least 100PSI)
 
A badly clogged muffler/spark arrester will cause very, very poor running.
 
Try a spritz of carb cleaner down the carb to see if it'll kick..
 
Maybe 2 teaspoons of 2 stroke oil down the cylinder may help it light off if compression is low..
 
Hold the throttle WIDE OPEN when pull starting. The engine may be flooded and this will often help it to start