I can attest to that with a 650 AVS2 on a street dominator with headers. I never did get the secondary side richened up to where it needed to be before I decided to go with a spread bore double pumper. The primary side responded well to one size up on jetting and then next smaller size metering rod, which is more than a little increase. I did have to put stiffer springs in from the tuning kit for the high idle vacuum (around 16 inches, leftover stock vacuum and lift rule limited oval track cam).
