[olddog]

Reversion air flow happens at idle (low rpm) with higher valve overlap cams. The intake valve is opening, when the piston is still moving up. At higher rpm and power the exhaust gasses have enough mass and momentum to crate a vacuum and pull air through the intake valve. At idle this does not happen and the piston shoves exhaust gasses out the intake valve. This blows air and fuel backwards through the carburetor. A typical single carburetor manifold has long runners and a plenum that adds up to a lot of volume, compared to Webbers. The volume dampens the affect. The Webbers have very little volume, and the reversion flow causes a haze of fuel to float above the carburetors at an idle.

The reversion flow not only makes tuning the fuel air mixture difficult, that haze of fuel only needs a spark to make for a very bad day.

Let the experts guide you here. Red neck engineering does not mix well with Webbers.