69 383 Performance
Sorry to barge in asking stupid questions but this caught my eye. Would you care to elaborate on this? I've never heard of this before and don't know what it means.
/n00b
Carter style (now Edelbrock) 4 barrel carbs have metering rods that stick through the main jets. The metering rods have steps of different diameters. The AFB style has 2 diameters and the AVS has 3. I'm pretty sure the Thermoquad has three also. Vacuum working against a spring on the top of the metering rods varies the depth of the rod into the jets. The fat part of the rod will flow less fuel than the skinny part of the rod because the fatter rod reduces the area of the jet.
Quick illustration:
Put the tip of your left index finger and thumb together so they form a circle.
Put your right thumb through the circle. Notice the area that is open.
Now put your right "pinkie", or fifth finger, into the hole. The open area is larger than when the thumb was there.
Imagine the circle being the hole in the main jet and the thumb and fifth finger a metering rod with 2 diameters. A smaller rod diameter will allow more fuel to flow (power) and a fatter rod allows less fuel flow. (idle and cruising) Voila!
A Carter, or Edelbrock, tuning kit has multiple main jets, metering rods, and metering rod springs. You can download a chart that shows most of the combinations available. See Summit or other places for the parts.
