Six pack outboard carb question

[dan juhasz]

I bought a set of old in the box Holley remanufactured outboard carbs for my A12. I went over the basics and refreshed a few seals and gaskets before the install.
There is a big difference in the way the outboard carbs come in compared to the re issue holleys that were on the car. Vacuum chambers were checked for holding vacuum and both have stock springs that are pretty light.
I think the re issued carbs had some modifications. I’m brainstorming about the function and application of the outboards. They get their signal from the center carb via the passage into the venturi. My question is about the same passages that are drilled in the outboards. Can they be modified ( ie made smaller ) to not act as a vacuum bleed ? I’m assuming that before those throttle blades actually open and start creating a vacuum also to the pods they are acting as a bleed to ease or delay the opening of the outboards.
Appreciate any input.
Dan

 

[PurpleBeeper]

Hmmmm….I don’t think the outboards act as an air bleed??? The easiest way to restrict the air flow to/from the outboards would be to insert something inside the hose with a hole drilled in it. There used to be some kind of “fix” where BB’s were put inside the holes at the outboard nipples, but I wouldn’t recommend them

 

[dan juhasz]

This hole goes from the Venturi body directly to the passage that supply vacuum to the diaphragm’s . Each outboard has it. For instance if you want to check if the diaphragm hold vacuum you apply suction to the nipple and hold a finger over this hole. If it’s not covered it bleeds off the vacuum as fast as you can pump the Mityvac.
So my thought is the other set of carbs had a modification to the size of this hole to make the secondary’s much more sensitive to applied vacuum from the center carb.
I can swear I read an article somewhere that said a mod was to tap in a lead split shot into that opening with diaphragm housing removed and reduce the size of the opening considerably.
I can’t find that read anywhere.

 

[lewtot184]

You're talking about the kill bleeds. Blocking or trying to reduce their size can cause the carbs to flop open instead of having a regulated opening. They also let the vacuum pods fill with air quicker when closing the throttle after a full throttle run. Basically don't mess with them. Regulate the opening rate with the springs. Definitely never put a check ball in the vacuum pods. If the carbs have "-1" after the list number they should have any necessary modifications.

People with 6paks are always looking some kind of modification for fuel or air. This is a street performance set up not a race intake system and should be kept as such. The only major modification I'd ever do to them is richening the center carb main metering and especially the idle circuit. Secondary idle always needs some enrichment with the mixture screws. The intake manifolds usually never fit properly.

 

[Bird 426]

What color are springs? Stock springs are not light. There are 6 different color springs.

 

[lewtot184]

What color are springs? Stock springs are not light. There are 6 different color springs.

Oem '69 carbs used a purple spring, oem '70-'71 carbs came with yellow. Neither are heavy springs like the 427 chevy carbs used.

 

[BSB67]

Several things:

1) make sure the outboards are opening smoothly and freely. With the vacuum line from the center carb, with your lungs you should be able to easily suck them open. Throttle plates can stick, and the throttle shafts can bind.

2) make sure there are no leaks in the vacuum pods.

3). You can use the yellow tip springs. I used white too.

4). check the kill bleed size. Larger = slower opening. Smaller = faster. Some are 0.050”+, I.e. slower. Start with 0.043”. I’ve been as low as 0.030” in both and I’ve plugged just one. They open crazy fast.

 

[dan juhasz]

Several things:

1) make sure the outboards are opening smoothly and freely. With the vacuum line from the center carb, with your lungs you should be able to easily suck them open. Throttle plates can stick, and the throttle shafts can bind.

2) make sure there are no leaks in the vacuum pods.

3). You can use the yellow tip springs. I used white too.

4). check the kill bleed size. Larger = slower opening. Smaller = faster. Some are 0.050”+, I.e. slower. Start with 0.043”. I’ve been as low as 0.030” in both and I’ve plugged just one. They open crazy fast.

I checked the kill bleed size today they are .046, which I believe is stock.
I ordered 2 white springs today if I’m still not happy I’ll move on the the kill bleeds. I’ve read even small changes make big differences. Like you mentioned .043 seems to be the suggested modification.
The diaphragms are new and hold fine, unless I hold the kill bleed closed with tape I can’t overcome the tension of the long yellow springs that are currently in the pods by me sucking on the vacuum hose.

 

[BSB67]

.. I can’t overcome the tension of the long yellow springs that are currently in the pods by me sucking on the vacuum hose.

Hmmmm.

Mine snap right open, pulling the center carb open with them.

 

[lewtot184]

If you can't easily pull open the pods with yellow springs something is wrong. Check the throttle blades to make sure they're not sticking.
1969 carbs had a slower opening rate due to larger kill bleeds and a smaller flow orifice in the center carb. In stock configuration they are very smooth opening, especially with heat in the intake. 1970 carbs and especially -1 carbs have smaller kill bleeds and can be made to open fairly aggressive. Blocking the kill bleeds thing started with A12 cars, but eventually people quit doing it as holley made changes to the carbs. As I think back I'm pretty sure my first set of carbs were 1970's and this back in either very late 1969 or mid 1970. I've tried all kinds of things with them but have pretty much settled with the factory design as the all around best performance for me. Center carb idle circut? ; that's a can of worms.

 

[dan juhasz]

If you can't easily pull open the pods with yellow springs something is wrong. Check the throttle blades to make sure they're not sticking.
1969 carbs had a slower opening rate due to larger kill bleeds and a smaller flow orifice in the center carb. In stock configuration they are very smooth opening, especially with heat in the intake. 1970 carbs and especially -1 carbs have smaller kill bleeds and can be made to open fairly aggressive. Blocking the kill bleeds thing started with A12 cars, but eventually people quit doing it as holley made changes to the carbs. As I think back I'm pretty sure my first set of carbs were 1970's and this back in either very late 1969 or mid 1970. I've tried all kinds of things with them but have pretty much settled with the factory design as the all around best performance for me. Center carb idle circut? ; that's a can of worms.

With the white springs if I'm testing each carb individually I can open the secondary's. If I try with both hooked up I can't overcome the loss at the kill bleeds. You mentioned the size of the flow orifice of the center carb. If that orifice is enlarged by a couple thousands would it supply a stronger vacuum signal to the pods and in turn open the outboards at a quicker pace? If so it seems like a better play than trying to make the kill bleeds smaller. If overdone you could always play with stronger springs.

 

[lewtot184]

With the white springs if I'm testing each carb individually I can open the secondary's. If I try with both hooked up I can't overcome the loss at the kill bleeds. You mentioned the size of the flow orifice of the center carb. If that orifice is enlarged by a couple thousands would it supply a stronger vacuum signal to the pods and in turn open the outboards at a quicker pace? If so it seems like a better play than trying to make the kill bleeds smaller. If overdone you could always play with stronger springs.

The 1970 and up carbs do have a larger orifice than 1969. Problem for me is i don't remember the difference. Chased that over 50yrs ago. Perhaps you're over thinking this. Intake manifold temperature can be a major player. Trying to suck them open orally versus the vacuum pull of 440 cubes at 2-3 thousand rpm is a whole different ball game.

 

[dan juhasz]

The 1970 and up carbs do have a larger orifice than 1969. Problem for me is i don't remember the difference. Chased that over 50yrs ago. Perhaps you're over thinking this. Intake manifold temperature can be a major player. Trying to suck them open orally versus the vacuum pull of 440 cubes at 2-3 thousand rpm is a whole different ball game.

I'm just trying to get back to the performance level and feel I had with the re issue Holley's that were on it. Today I received the ProMax throttle plate, installed it , put in the 2 white springs, set up the idle and mixture and went for a drive. It's much better with the lighter springs, and it feels like a seamless transition to all carbs participating albeit at a higher rpm range. Whatever mods were made by the guy who set up the re issue Holley's if you were cruising at 50/55 and just leaned into the throttle to pass ( no flooring it etc ) you immediately felt the outboards kicking in and it pulled like a freight train. I like to get back to that.
I have the 4376 1970 center carb for sale on this site, I can remove the pod and gauge the size of the feed orifice and compare it to the 1969 4392 that I'm working with.
But what I asked before would a larger sense orifice in the center carb produce a stronger signal to the pods?

 

[lewtot184]

I'm just trying to get back to the performance level and feel I had with the re issue Holley's that were on it. Today I received the ProMax throttle plate, installed it , put in the 2 white springs, set up the idle and mixture and went for a drive. It's much better with the lighter springs, and it feels like a seamless transition to all carbs participating albeit at a higher rpm range. Whatever mods were made by the guy who set up the re issue Holley's if you were cruising at 50/55 and just leaned into the throttle to pass ( no flooring it etc ) you immediately felt the outboards kicking in and it pulled like a freight train. I like to get back to that.
I have the 4376 1970 center carb for sale on this site, I can remove the pod and gauge the size of the feed orifice and compare it to the 1969 4392 that I'm working with.
But what I asked before would a larger sense orifice in the center carb produce a stronger signal to the pods?

Too your last question, yes. What I'm trying to get at is there's more to it than just orifice sizes.

 

[RJRENTON]

I'm just trying to get back to the performance level and feel I had with the re issue Holley's that were on it. Today I received the ProMax throttle plate, installed it , put in the 2 white springs, set up the idle and mixture and went for a drive. It's much better with the lighter springs, and it feels like a seamless transition to all carbs participating albeit at a higher rpm range. Whatever mods were made by the guy who set up the re issue Holley's if you were cruising at 50/55 and just leaned into the throttle to pass ( no flooring it etc ) you immediately felt the outboards kicking in and it pulled like a freight train. I like to get back to that.
I have the 4376 1970 center carb for sale on this site, I can remove the pod and gauge the size of the feed orifice and compare it to the 1969 4392 that I'm working with.
But what I asked before would a larger sense orifice in the center carb produce a stronger signal to the pods?

First....there are no such things as "pods" on Holly carbs (like dizzies for distributors or Eddys for Edelbrock)....they are called VACUUM DIAPHRAGM ASSEMBLIES....pods are part of a bean or pea plant. LEARN THE CORRECT NOMENCLATURE. The vacuum diaphragm assemblies receive their opening signal from the primary carb's venturi differential pressure suplanted (assisted) by the end carb's venturi differential pressure ORIFICES, via a check ball/controlled bleed orifice. THE END CARBS DO NOT PULL OPEN THE CENTER CARB....They, the end carbs, operate strictly on differential venturi pressure (the greater the differential pressure, the faster the opening rate will be). The primary carb (center carb) have linkage that forces the end carbs closed on primary carb throttle closure, if the end carbs are open. The primary carb's venturi bleed office size will determine the opening point (based on differential pressure) combined with the outer carb's vacuum diaphragm spring tension will determine the RATE THE END CARBS OPEN. The HOLLEY book, by HP BOOKS explains in depth HOW the model 2300 Holley carb operate with correct descriptions.....I suggest you read it......a wealth of knowledge. There have been volumes written about how to tune Holley six barrel carbs......FYI..........just my opinion......
BOB RENTON