Date registered: Aug 2009
Vehicle: '72 250C, '74 280C, '85 500SEL, '81 300CD.
Location: Tucson, Az.
Mentioned: 2 Post(s)
Quoted: 49 Post(s)
Okay guys you are on the right track.
Luna, the open hole is where you need to "tee" into the vent line with a "filtered" open vent. You are trying to achieve a low pressure area and not a complete vacuum. My camera is out on loan or I'd give you some visual ideas.
So,install a "tee" where you have the vent hole, connect the tank vent line to one end of the "tee" and an open, filtered, fitting on the other. It can be as simple as a wrap of foam rubber.
You don't want to leave the hole just open as it is sucking unfiltered air. It's no worse than what you were doing before you connected the hose but it's not right.
"K", the reason you are hearing the leak is because you've turned the crankcase into a vacuum reservoir. Add the additional vent as Luna did to resolve the problem.
The fuel/air system you have is designed for the open suction center hose but it does need some restriction to be correct.
The original air cleaner system did this and you need to recreate the conditions using the free flow K&N's.