It depends on what model we are talking about, on the hobby saws 137/142/235/240 it is a duck bill valve witha sintered plug above it, the bigger saws either have a white plug ( VION ) this is a porus material and very rarly blocks , the latest machines have a white valve pressed into the tank on the r/h side of the saw, this vave has a nipple on it, some machines have nothing connected to this, and some machines have a pipe which goes to atmosphere. If the machine has a fuel primer bulb, do not connect the return hose from the primer to the nipple on the tank breather. The only answer is to replace the breathers if they do not function, using an air line on them will destroy them and the tank will then leak, the latest breathers are very tight and block easily ( this is due to new gas emmission laws)
Husqvarna man, October 2009
