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.