Holley secondaries won't open

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dman

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I've got a holley 4 bbl 750cfm (pretty sure it's a 4160), electric choke, vacuum secondaries. It's on a 318 with a 2 bbl intake and a 4 bbl adapter. I replaced the choke and cleaned the carb a couple weeks ago. I had to replace the secondary connecting rod because a buddy said the reason the secondary barrels won't open is because the rod needs to be bent :banghead:. I can open the barrels manually and the butterfly valves don't hit anything. But when I open the barrels by hand with the throttle linkage, the secondaries never open, not even a little. The secondary con. rod will move down but it won't move the rod that goes to the diaphragm. It starts up first time but it sounds like it's running rich (if I hit the throttle sometimes, it will bog down and almost stall out). Maybe that has something to do with the back barrels not opening? Thanks in advanced to anybody that can help me out
 
You can't check for secondary operation on a vacuum secondary Holley by winging the throttle by hand.

They only open under load.
 
I haven't rebuilt the pod. The same guy that said bend the con. rod told me I shouldn't open the diaphragm when I was cleaning it. I've put the carb underload while it was running and they didn't move. Is there anyway to tell what's wrong without driving it? I've heard about the paperclip trick but the car can't be driven right now. Should I just replace the whole vacuum pod? Or would some sort of vacuum leak cause a problem if they open from vacuum? If I had the money I'd just buy a carb with mechanical secondaries, they seem more straight forward.
 
Lookit it will not move on its own idling,you can rev it and manually get it too work hold the throttle wide open and then put your finger under the diagram move it up that will get your attention.
 
Take a paper clip and attach it to the secondary diaphragm rod that comes out of the diaphragm and connects to the throttle shaft. Slide the paper clip so it is all the way up against the bottom of the diaphragm. Drive the car and accelerate enough so the secondaries would open. Come back and take note of where the paper clip is. If it has been pushed down from where you put it, the secondaries are opening. If it is in the same position they are not. Report back and we can go from there.
 
A thought that comes to mind is that you are trying to run thru a 4bbl to 2bbl adapter; I can under stand budget, this is what you've got, etc. It could be a portion of your pain.

I've run a Holley 3310 on a 318 in the past with good success, it takes patience. You haven't mentioned what spring you are using, there are 6 different possibilities, they go:
white the lightest
yellow
purple
plain (kinda silver)
brown
black the heaviest
This is one list I have; another list goes like this:

Yellow (short spring) Lightest
Yellow
Purple
Plain (standard spring)
Brown
Black Heaviest
A lighter spring will open the secondaries sooner; open too soon and it's a major bog, go to the next heaver spring. The secondaries should not open late with sudden surge like some one fliped a switch. When you get it right, you almost can't tell the secondaries have opened, it's a smooth steady pull with you right foot to the floor.

Make sure the diaphram isn't torn, the secondaries will never open if it is.
 
Why do you think they are not opening? As stated before, the secondaries will open under load, ie. driving, not revving in your driveway!
 
Think of the flow rate on a vacuum secondary Holley as being an "up to" number. That's why you can bolt a fairly large carb and still have smooth street performance. The carb will only flow as much air as the engine requires.

In the original post you pretty much identified the problem. A stock 2 barrel intake is like a restrictor plate. The primaries on that Holley will flow about the same as the mounting flange on that manifold. Grab a Performer intake off eBay and a lot of your problems will go away. But if you still have a stock cam and exhaust don't expect miracles
 
There is no reason to not take the vacuum assembly off and no reason to not dissassemble. If that other guy thinks the rod needs bending....then you need to stop listening to that guy!

It is easy to test: Take it off the carb and you will see a small air passage hole in addition to the mounting screw holes on the flange where it mounts to the carb. Place a small hose with a clean, straight cut end surface tightly over this hole so that it is well sealed (vaccum hose works well) and suck on it; the rod should move and you should not be able to suck any more air. Try to hold the vaccum by moving the tip of your tounge to seal the hose; the rod should not retract. (Or rig up a vaccum source to do this; the hard part is sealing the hose against the vacuum assembly.)

If this does not work then either:
- the small check ball inside is stuck and not allowing vaccum to pass through the air passage in the mounting flange to reach the diaphragm
- the diaphragm is busted if you can continually suck air

You can disasseble these easily; just be careful to not have the screws snag the diaphragm while turning them and tear it. Also, check the seal of the vacuum assembly against the carb body where it mounts up to the body.

A normal vaccum leak in the intake below the throttle plates has no effect on this unit becasue they do not work from that vaccum. These work by vacuum generated in the carb throat ABOVE the throttle paltes that is generated by airflow down the carb throat. The reason it is hard to impossiblwe to activate these secondaries whil sitting still is that you can generate this throat vaccum only very briefly by opening the throttle sitting still, but you cannot create the needed level of throat vaccum for long enough without the engine over-revving and blowing up. This vaccum has to exist for a certain amount of time to move the diaphragm and you can't do it long enough just revving the engine.

If the diphragm checks out good off the carb, but the paper clip test does not show it moving, then the air passage inside the carb from the mounting flange on the body down into the primary throats is probably blocked. Shoot some carb cleaner into the air passage hole where the vaccum assembly mounts to clean it out as se if that fixes it.

These are really not all that hard once you know how they work. Good luck and let us know how it turns out.
 
C130 Chief said:
Think of the flow rate on a vacuum secondary Holley as being an "up to" number. That's why you can bolt a fairly large carb and still have smooth street performance. The carb will only flow as much air as the engine requires.

In the original post you pretty much identified the problem. A stock 2 barrel intake is like a restrictor plate. The primaries on that Holley will flow about the same as the mounting flange on that manifold. Grab a Performer intake off eBay and a lot of your problems will go away. But if you still have a stock cam and exhaust don't expect miracles
Click to expand...
A lot of wisdom here IMO. I am not sure that the stock 2bbl intake flange is THAT restricted but is certainly not going to flow anywhere close to 750 cfm.

And good question on the cam. I put a 4bbl carb AND 4 bbl manifold on an old Ford 292 truck engine once way in the past, and the change was not very noticeable. That low duration truck cam made it pretty much a waste of effort. So, the OP can help to tell if he has a cam in this engine.
 
Thank you to all the replies. I've worked on a lot of carburetors but never on a car so when I'm looking over everything, and don't see the secondaries moving, I thought something was broken.

nm9stheham, you hit the nail on the head. That's exactly what I was looking for. I needed to know how it worked and how to test it, and you cleared it up. I'm going to test it out off the carb, then try the paper clip trick if that checks out ok. I guess it's a stock cam, the guy I bought it from never mentioned anything about putting a cam in. I'm trying to see if a 4 barrel manifold is in the budget. I've seen some of the performers for under 100 on ebay. I don't know if it's worth it if I can't get a cam as well, if it won't make a difference. Maybe I should get a smaller 4 bbl? Or go back to a 2 bbl?
 
A 4 barrel w/intake, an mild cam and dual exhaust will make a noticeable difference on a 318. Something like a Comp XE262. Has the engine ever been apart? If not, you want to replace the timing chain and cam sprocket ASAP.

A 600 CFM carb is probably enough for any mild 318. Sure the 750 will work, but it won't be any faster.
 
Yes, a 600 cfm will be good for 300+ HP easily. I like vacuum secondary types because they drive better on the street and give better mileage in general, and works fine in my experience. I used to get 300+ HP from a 351C with a torque cam and 600 cfm Holley vacuum secondary carb, yet get 19-20 mpg in the highways. (Had some good aiflow mods too.) But, I never run engines to max possible HP either.

I was also thinking that a 500 cfm 2 bbl on a 2 bbl manifold that has been blended at the flange will do quite well, and should get you all that you can get from a stock cam and most mild cams too for 318 ci. This combo is common on circle track racing for limited HP V8 classes. The 500 CFM Holley is easy to tune. It might not be quite as driveable as the 600 cfm vacuum secondary though, as you don't have the small primaries which keep good airflow and operation at low loads and RPM's.
 
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