THE ULTIMATE PERFORMANCE CARBURETOR Designed and calibrated for small cubic-inch engines and dual-quad applications such as our RPM Dual-Quad Air-Gap, Edelbrock C-26, F-28 and Street Tunnel Ram. For single carb applications, match with an Edelbrock Performer or Performer EPS manifold or other brands of similar design. Includes both timed and full vacuum ports for ignition advance. #1901/#1902 are calibrated for single-quad applications and factory equipped with: Metering Jets - Primary . 095, Secondary . 095, Primary Rod . 070 x . 052, orange spring (5' Hg). #1903 is calibrated for dual-quad applications and factory equipped with: Metering Jets - Primary . 095, Secondary . 077; Metering Rods - . 070 x . 052; #1904 includes Primary . 095, Secondary . 077; Metering Rods - . 070 x . 052; Step-Up Spring - orange (5' Hg).  Use carb Studs #8008 or #8024 if needed.  Match with an Edelbrock intake manifold for the ultimate induction upgrade. ** INSTALLATION NOTE: Manual choke AVS2 Carbs cannot be converted to electric choke. Carbs #1903, #1904 and #19034, #19044 are calibrated for dual-quad applications only and need to be purchased together, one manual and one electric. For single carb small-displacement engines and Street Tunnel Ram applications use carbs #1901, #1902, #19014 and #19024.