I understand that the basic function of the flame trap is to vent excessive crankcase pressure, and unburned gases, back into the intake flow. Looking at the top of the flame trap assembly, there is a second, smaller-diameter vacuum hose that goes to a fitting on the intake manifold. Does anyone know the purpose of this second line? Just wondering.

Leon

'86 244DL 182K

It supplies vacuum to the PCV system at idle, when the intake system is practically at atmospheric pressure. The vacuum is restricted by the fitting on the manifold, but this restriction also means that it clogs easily and should be checked every time you check the flame trap. Contrary to the other poster's assertion, crankcase fumes do indeed pass through this fitting.

That line is a vaccume line and what it does is pull a vaccume on the flame trap valve to induce a vaccume draw and as it is designed will not pull any fumes into the vaccume line itself because the reduction nipple at the intake manifold restricts its ability to pull a full vaccume on the flame trap valve. It helps pull up and direct the fumes from the crank case. Without it your engine will get gummed up. Hope this helps.