Quote:
Originally Posted by svandamme
Well i explained in my post that vacuum leak can cause lean running 4 stroke engines , and when a high comp 4 stroke engine runs lean, it can cause among other things, detonation.
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An intake tract leak on a 4-stroke will cause lean running, but a bottom end vacuum leak? That's 2-stroke territory because there is little to no vacuum in most all 4-stroke crankcases as most 4-strokes have the crankcase open to the atmosphere through the breather. Most 4-strokes use a PCV valve to prevent an excess of air flowing into the intake tract. I keep saying most because there are exceptions. Like the road draft tube on my old Studebaker.
Quote:
Originally Posted by svandamme
Again, nobody said anything about 2 strokers, and the comment about vacuum in the bottom end did not automatically imply 2 strokes either because the crank breather ties into the vacuum system of most 4 stroke FI engines.
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The crankcase breather is almost always open to the atmosphere through the air box. Crankcase vapors in excess of what the PCV valve can handle flow through the breather and into the intake upstream of the throttle. There is no vacuum upstream of the throttle aside from any filter and ducting restrictions.
