Just an addition here if I may. The box stock Holley 1850s come through with the "universal" throttle arm on the primary throttle shaft. When used in a dual quad setup using the original Ford FE dual quad linkage which is a progressive setup, the secondary carb must open at a quicker rate than the primary carb. For instance, the primary carb opens 100% beginning with the first depression of the accelerator pedal and ending with the pedal to the metal position. The secondary carb begins to open when the accelerator pedal is approximately one-half way through its travel and must be open 100% when the pedal is fully depressed. Therefore, the radius (distance) between the pivot and the trunnion (stud that the linkage attaches to) must be shorter on the secondary carb to allow for a quicker opening. I hope that makes sense.
Anyway, I had the same problem on my 351W using a Price Motorsports dual quad intake and a pair of 390 cfm Holleys and FE medium riser dual quad linkage which externally have the same dimensions as the 1850s. I actually swapped the throttle arms from the universal ones to Ford pattern arms and the setup works beautifully. Rather than post everything here, if you are interested in what I did just click on the link to
Page 6 of my Cobra Build Site and scroll down about half the page. I purchased Ford style throttle arms direct from Holley. You would need access to an accurate drill press to drill into the end of the primary throttle shaft but the end result is well worth the effort. Your carbs will both look and operate correctly. Below are the photos of the primary and secondary throttle arms so you can see the difference in the placement of the trunnion position. Placing the trunnion closer to the pivot point causes the secondary carb to open at a faster rate than the primary carb.
PRIMARY THROTTLE ARM
SECONDARY THROTTLE ARM
UNIVERSAL THROTTLE ARM REPLACED WITH FORD THROTTLE ARM
