<VV> Poor idling

[Kenneth Schifftner]

Bill/others:

From my experience, you should not be seeing fuel dripping from the cluster.  At idle, the cluster is just sitting there ready to do its thing...off idle.  The idle mixture is created in the well under the cluster then is injected (actually pushed through by atmospheric pressure) to a point below the throttle plate.  To get there, the mixture is metered by the idle mixture screw.  Bob Helt had a great description of this in one of his books.

If the cluster is weeping, I suspect an excessively high float level...but likely by only 1/16th inch of so.  Another cause could be the aspirating port for the tube that is in the well under the cluster that creates the idle mixture.  That tube can get plugged thus blocking the mixture. If the head is cold on the side of the trouble carburetor, it is a sign that fuel flow is lacking. No fuel, no heat.

What I do is remove the idle mixture screw entirely while the engine is running then with gloved hand over the carburetor inlet, open the throttle for a few seconds then remove the gloved hand. That causes abnormally high vacuum at the mixture injection point.  I then put the idle mixture screw back in, turn it out 2-3 turns, then repeat the gloved hand thing.  Doing that puts an abnormally high vacuum at the air bleed port for the idle mixture tube.  I also spray carb cleaner into all of the bleed ports located on the top of the cluster.

With a carburetor, a dispersion of air and fuel is used...not just fuel being pulled of pushed into the air stream. At idle, that dispersion is created by the tube located in the well under the cluster and by air being mixed with the fuel in that well.  Off idle, the fuel is mixed by the high gas velocity produced by air movement through the carburetor venturi.  The spiders of the cluster move the fuel and some air towards the venturi wall for better atomization.  At idle, however, if the cluster spits, large fuel droplets go into the engine and poor combustion can occur.

Hope that helps.

Ken Schifftner
NJACE and SDCC