100psi sounds low to me, all my saws are 150 - 175 psi, I would suggest taking the silencer/muffler off and look at the piston for signs of seizure. A new piston with no rings will make 70psi.
May be worth taking the barrel/jug off and checking that the ring isn't broken or the piston isnt shot - new non Husky piston is circa £23 on the bay.
Steve, May 2009