Jeremy58Jeremy

Hey Guys,
I have a holley with mech secondaries on my 454 and am having trouble getting them to open all of the way. I don't have enough throw on my accel. linkage to get all four barrels 100% open. Does anyone know if there is a different ratio secondaries linkage that would allow them to open with a shorter cable throw. Anyone run into this or have any guesses. My accelerator pedal is in good shape with no slop, it just runs out of room before WOT on the carb. I need about an extra 3/4 to an inch of throw to get the secondaries all of the way open. Thanks for your help, hopefully some of you carb Gurus have some ideas!!

midyearvette

sounds like your linkage connection is too high on the throttle lever...drill out the lower hole just below the large hole usually used for linkage......if you mess with the secondary linkage you could un cover other issues....iam assuming the front two barrels are not opening all the way either??.....good luck

Jeremy58Jeremy

Yea, I'll have to look at that, the linkage is attached pretty high on the carb. The linkage isn't progressive, the secondaries only start to open when the primaries are at 100%

midyearvette

if the primaries are FULLY open, then the secondaries should be too....think about it ...if the front is fully open, then the throttle lever is against the stop...holley does make different linkage hook ups for the dp"s but check for full primary opening first, against the stop on the throttle bore housing...good luck

baxsom

what throttle cable are you using?
maybe your cable is too long.
i know when i got my 72 454, it had a square bore manifold and holley on it but was still using the stock cable, the stock cable wasnt allowing the throttle lever to go back all the way.

bashcraft

If the primaries are fully open, you're not going any further. Are you sure it's a mechanical secondary carb? Sounds like a vaccum secondary carb.

Jeremy58Jeremy

I'll try and describe it as well as I can, but I'm away from the car so I can't post pics. The primary throttle blades go to fully open and has a spring loaded stop that lets the linkage continue to rotate and open the secondaries. There is a stepped cam that lets the secondaries open at a quicker rate than the primaries, ie. shorter throw, but they do not start to open untill the primaries are 90% open, then the secondaries start to crack. With the propper amount of throttle cable pull all four barrels will go 100% open, my problem is that I can't get my cable to pull far enough to open the secondaries all of the way. Sorry It would be more helpful if I had pics, but my description will have to do, and yes.... it is a Mech. secondary carb, fur sure fur sure

jotto

Any chance your throttle pedal has got bent in the past thus not allowing full travel?
Do you have new mats or thick carpet down?

midyearvette

go back to my first suggestion of the linkage set too high on the throttle lever.....

toddalin

I just checked this on my 650 dp sitting on the shelf that works properly.

The secondaries start to open when the primaries are ~1/2 open. Yes, the secondaries are "stepped" and open at a faster rate than the primaries such that both the primaries and secondaries reach full open at the same time.

Jeremy58Jeremy

I'll have to take a look a mine and figure out what is going on, because my secondaries definately do not start opening that early. Mabey I have some bent up linkage parts or somthing, although everything looks like its in good shape. That why I was asking about different ratio cams, It just didn't seem right that they were opening up that late. I'll monkey with everything when I get back into town and see if I can make any progress, thanks for all of the replies, I have a couple of ideas on what I need to do now.

OMF

you can adjust the secondary opening point by bending the short link. I adjusted mine that way on a 600 DP.....a few years ago now so its not front and centre in the memory bank.....otherwise I'd be more specific.

Jeremy58Jeremy

This is along the lines of what I was looking for. I figured I could modify that part of the linkage, but am trying to work out in my had just how to do it. Thanks for the tip!!

toddalin

The Holley manual notes that "Secondary opening is delayed until primaries have reached approximately 40% of opening."

I was looking for how this is adjusted, but am not seeing it in the manual.