i just rebuilt my carb. secondaries will not open at all. where does the carb get the vaccum to open?

 

You'll probably never "see" them open when you work the throttle with it sitting still, as they open on demand by vacuum, and the engine doesn't work hard enough just cracking the throttle to open them- if they did open at that point, you'd probably have a bog when they open when actually driving it. If vacuum secondaries are functioning correctly, you won't really "feel them kick in" as is often said, should be smooth & seamless, as the vacuum signal tells the carb that the engine can use more flow.
4100's and Holleys are pretty simple, if the correct gaskets are installed correctly, all the passages are clear, diaphragm is good, and the linkages right, it should work OK, as long as the carb size is matched to the engine size. Size shouldn't be a problem with a 4100, as the largest 4100 will work fine on a 289-302, and very well on a 360-390

 

the carb is factory for my 66 352 i just rebuilt it my first time doing that. the secondaries will not open under load. rigged it up to work on a string now it works fine. I did not soak the casing and lid in cleaner. rookie mistake, i thought the secodaries were mech. is the vaccum tube that works the secondaries the tube that runnes from the primaries to the secondaries on the lid.i used all the same gaskets that i found in my carb as the kit came with what was about 3 differnt lid gaskets and so on

 

turtle, one of the common problems with both the Autolite 4100 and the Holleys is either pinching the edge of the diaphram or not getting it all the way sealed.

FWIW, I will post the "check" method I have used for longer than I care to state.

On the Autolite, before you reinstall the top (bowl cover), open the primaries (have the fast idle lever on the choke side off). Push the lever coming out of the secondary diaphram housing all the way to full open. Cover the small hole in the bake of the float bowl with your finger. It should hold the secondaries mostly open and stay that way until you open the hole. If you want a real good test, after everything is together, hold the choke and primaries wide open and use an air nozzle to blow down past the signal tube, the secondaries should open up nicely, than close when the vaccum signal is removed.

For Holleys, after assembling the secondary diaphram and before mounting it to the carburetor, push the diaphram rod all the way in and cover the vacuum port near the front mounting screws with your finger, release the rod, it should stay up in the housing. Like the Autolite, after assembly, with the choke and primaries wide open blow air down the choke side primary bore, the secondaries should open (you may have to "play" with the air flow position as Holleys have a small hole in the side of the venturii and some have a bleed hole just above it in the top of the venturii).