Fixit-
The adjust-a-jet kit allows you to effectively change primary jet sizes with the turn of a screw. By using metering rods instead of jets, you can change the mixture simply by turning the metering rods while the car is running. For some reason, I could not get Holley's website to work, but below is a link to someone that is selling one of the kits on ebay.
http://cgi.ebay.com/ebaymotors/ws/eB...tem=2437152038