Have a look in the 700-series FAQ's. I forget what it's under, but it was not too hard for me to find when I needed it.

A "breather box", maybe about 3"x3"x4", is attached to the crankcase side using several screws. This is approximately below the intake manifild's #2 port. Pretty far down.

A hose about 3/4" outside diam. rises from the breather box and comes up between the intake manifold and the valve cover. There you will find a fitting with a 3 way connection. One thinner vaccuum line goes to the intake manifold, the other thicker line goes to the side of the main air intake duct.

Th 3-way connector comes apart, you should find the flame trap inside. Older ones used metal, now it's plastic. Clean with carbeuretor cleaner. Also clean the hoses, and the small nipple on the intake manifold. Clean the breather box if you can get it off. You'll need patience and a rubber wrist.

I cleaned a breather box with a lot of carb and brake cleaner, and lots of shaking and tapping of the box. Poked screwdrivers inside to break up the crud. If a Volvo or import-parts dealer will sell a box for a fe $$, that would be a good purchase.