Newbie here to this forum so bear with me. I have a 64 1/2 with the code "D" 289 and 4 barrel carburator. With the engine off and the throttle held open, the secondary actuator lever can then be manually moved. My question is, should there be fuel pumping into the secondary venturies when I do this like occurs on the primaries when manually moving the throttle actuator? I'm not totally convinced that my secondaries are opening and if they are, they are delivering fuel. I saw a suggestion on one forum to fix a piece of string or tape to the secondary actuator, go for a test drive, floor the throttle and see if the tape or string is pulled loose or broken. My secondaries are NOT pumping fuel onto the throttle plates (engine off) when manually moving the seconary actuator rod, but I don't know if they should be.
There is not any accelerator pump on the rear two venturies. It should draw fuel thru vacuum produced when open and running.
Under normal conditions, just reving the engine with no load will not get them to open.
What I have done in the past is locate the linkage that has to move when they open. I put a small amount of grease on the slide portion and drive the car. Upon returning, I look for a change in the grease. Some have used a paper clip but I don't like the idea of it getting mixed up with the linkage and causing problems.
A 4100, properly jetted and setup/tweaked/tuned for a specific application will never give you a seat of the pants "kick" that some other carbs may give upon opening the secondaries, but WILL give excellent smooth performance with reasonable fuel mileage (if you keep tour foot out of the secondaries) and great driveability. The lack of a "kick" is a good thing, as the "kick" is actually a slight bog before more acceleration. There are ways to get the secondaries to open earlier (I'm not sure what needs to be done). There is also a mod to make the secondaries mechanically operated, but seeing as there is no accelerator pump on the secondaries, I don't really see the point/advantage. If your secondaries don't open, upon testing, there is ether a plugged/clogged vacuum passage or the diaphragm on the rear of the carb is bad.