AVS2 tuning

The paragraph below is straight from the carb tuning guide. If you think the second step of the metering rod is coming on to soon, use a weaker spring. See below as I believe you mentioned 13” of vac @ idle which means the factory installed spring in your carb is pushing the rod up at idle


• Measure the manifold vacuum at idle. It is critical that the Step-Up spring vacuum rating is always lower that the manifold vacuum at an idle, with vehicle in neutral. One option in choos- ing the appropriate Step-Up spring, is by reading vacuum at an idle, and using a Step-Up spring with a rating of half of what the vacuum reading is at an idle (Example: 14" of vacuum at an idle, would equate to a 7" (Pink) Step-Up spring. Note: Load-factors come into play as well, such as the vehicles weight, gear ratio, etc. The above example is simply a baseline procedure. If it is below 7" Hg, there is a good chance that the Metering Rods are in the up (rich) position. When combined with a high idle air rate this can cause the Nozzles to discharge fuel at idle. Use a weaker Step-Up Spring (see section on Step-Up calibration) to keep the Rods down at idle. With some cams, a stiffer spring (pink or silver) is necessary. Experimentation is the best way to determine which is best for your application.
One thing to do is to loosen the screw on the metering rod covers and twist them slightly and snug up the screw. That way you can check what’s happening with the rod. Also changing the rods without changing the jets will change the air fuel ratio.