Quote: Agree its high overlap (long duration + tight lobe seperation) that is the main factor. I suspect a single plane manifold makes it worse also.
Tuning can help clear it up... at least partly. Adequate initial advance plus the leanest AF that will hold a steady idle. Mine likes 20 degrees initial advance and around 14.5 air/fuel. Getting those two dialed in helped both vacuum and "fumes".
I use a single plane manifold and my car don't stink at idle. I run 22 degrees intial, I don't know why guys are afriad to run plenty of intial timing.
