Why can't I get my secondaries to open on my Holley 750 4160?

Question

Hi, I can not get secondaries to open on my Holley 4160 750 vacuum secondaries. I've replaced the diaphram, using lightest spring, cleaned vacuum passages. Am I just over-carbed? Specs: Chevy 350, Edlebrock RPM Performer intake, Cam lift - .440/.460, duration - 270/280, Trick Flow twisted wedge heads (63cc), timing - 15 initial, total - 36 degrees, 700r4 tranny with 2300 stall, 4.10 rear. No stumbles or bog off line. Will spin tires but not shread. Thoughts?

Answer 1

no vacuum to secondaries. pull off hose see if there is any suction

Answer 2

Then you are missing a piece of mechanical secondary linkage on the drivers side of the carburetor. Go on line and look at any street double pumper and you will see the bent arm that's missing. Now you have an excuse to buy a Holley 670 CFM Ultra Street Avenger with VACUUM secondaries. The onlt possible place for a double pumper is if you have a very light car with 4:11 gears or lower and a 4 - 6 speed transmission.

Answer 3

It's possible they could be opening very late, you could test a lighter spring, holley has a yellow spring and a white spring as the lightest, could go a step further and cut a coil off the white one. You could also test a real heavy spring to see if you get a hesitation, that'd be your secondaries. You would have better results with a 600-650 cfm carb especially if this is street driven.



Chevy racer is right, 2300stall doesn't match the combo. Swap for a 3000 stall, get a lockup if you're worried about mileage. If the transmission doesn't match the combo weird things happen with carbs. After a year of tinkering I'm still trying to tune my holley perfectly, if that's possible

Answer 4

How are you checking to see the sec. are not opening? If your not getting a bog then I don't see how they could be staying closed.



Are you looking down in carb and working throttle by hand? If so you will not get the sec. to open on a vac sec carb that away. It needs a load on engine to open.



Yes you are over carb'ed alittle but thats not your prob here. That cam could use more converter though, like 2600-2800 stall



When you go WOT do you get a bog or flat spot, or if tooling along then floor it, does it bog?



If the sec. wasnt opening you would get a bad bog