Secondaries don't hold vacuum with vacuum pump

[440beep]

I was doing some more tuning of my Six Pack and tested the Holley vacuum secondaries with a vacuum pump. The secondary throttle blades move a little when I'm squeezing the vacuum pump trigger, but the secondary doesn't get sucked open and stay open. I can hear what sounds to be a vacuum leak every time I squeeze the vacuum pump trigger coming from inside where the boosters and throttle blades are.

Is it only constant vacuum that holds the secondaries open, or should a hand held vacuum pump keep the secondaries open?

If it is leak, where should I start looking? I already checked the diaphragms and they are good.

 

[Beekeeper]

It's either the diaphragm or the housing that's leaking.

 

[silversedan]

there is a small bleed or signal hole in the venturi area connected to the diaphram vacuum circuit, that's where your hearing it bleed off, you'd have to take the diaphram off the carb to test it properly.

 

[440beep]

I'm hoping it's the gasket in between the diaphragm base and the main body that is the problem. Gasket looks to have seen better days. Hope it's merely bad gaskets and not the need for new main bodies.

On a side note, the car is pretty quick now and if the secondaries aren't at full potential I can only imagine once they are working properly. But the funny thing is that the secondaries are opening so they must be getting some vacuum.

 

[PurpleBeeper]

It's almost for sure that little gasket between the vacuum "pod" and the main body....those are a little tough to come by, but you can make one from some flat cork gasket sheet or what's left over around the edges from the gasket you get with a carb rebuild kit. When you apply vacuum to the secondaries, they should stay open until you release the vacuum.

 

[Jcharger]

you might be able to check whether they open when driving. I have seen various approaches using paperclips or bobby pins or grease on the rod below the vacuum canister. My guess is that if they open, they will stay open because there is a constant source of vacuum. The test also may give an idea of whether they are opening fully.

 

[440beep]

I just ordered those little gaskets from Chicago Carburetor, they had them!

And I need to do that paper clip trick with the secondaries once I fix them and see how they are opening. Currently they are opening (but how much?) because I can definitely feel it when they do open. Really keen to see how it is with properly working secondaries!!

 

[68 HEMI GTS]

Easy to test on the car, disconnect the outboard linkage, plug the kill bleeds with your fingers and suck on the main hose that goes to center carb. Kill bleeds are on the passenger side of the venturies.

 

[440beep]

Ok, you lost me. And this is testing what exactly? Plug which kill bleeds? Primary or secondary? And hook up vacuum pump to center carb vacuum hose?

Easy to test on the car, disconnect the outboard linkage, plug the kill bleeds with your fingers and suck on the main hose that goes to center carb. Kill bleeds are on the passenger side of the venturies.

 

[68 HEMI GTS]

Ok, you lost me. And this is testing what exactly? Plug which kill bleeds? Primary or secondary? And hook up vacuum pump to center carb vacuum hose?

this is to check that they will or do indeed open off vacuum. You could even do one at a time. Say you wanna check front carb.. Remove front linkage rod, hook your vacuum pump to front carb vacuum line only, plug kill bleed (front carb), I just use my finger but I suppose you could put some tape or something over it and see if it opens with vacuum.

 

[68 HEMI GTS]

If you think you are having intermittent vacuum issues check everything including lines and tee. I had a tee that had a pinhole in it. Sometimes the secondaries worked and other times not so much. Took a bit to figure that out...

 

[lewtot184]

it's the kill bleed. the carbs supposed to do this.

 

[440+6]

Easy to test on the car, disconnect the outboard linkage, plug the kill bleeds with your fingers and suck on the main hose that goes to center carb. Kill bleeds are on the passenger side of the venturies.

Exactly, or do the same to the carbs one at a time.

The kill blead is the small hole inside the venturi, if you stick your finger down the throat of the carb where the diagram bolts to it you will feel a small hole, it must be blocked to hold vacuum.

 

[440beep]

I hooked the vacuum pump directly to the secondary tube where the normal vacuum hose goes, and worked the secondary from there. The diaphragm arm would move a little bit every time I squeezed the pump trigger, but it would not open all the way nor stay open. I could hear the suction noise coming from where I think the diaphragm base connects to the main body, so hopefully its that gasket. But tonight will try doing the kill bleed test. And once the gaskets are replaced I wil hook the vacuum pump to the center tee and see how that works and also test the vacuum hoses.

If you think you are having intermittent vacuum issues check everything including lines and tee. I had a tee that had a pinhole in it. Sometimes the secondaries worked and other times not so much. Took a bit to figure that out...

 

[68 HEMI GTS]

You

I hooked the vacuum pump directly to the secondary tube where the normal vacuum hose goes, and worked the secondary from there. The diaphragm arm would move a little bit every time I squeezed the pump trigger, but it would not open all the way nor stay open. I could hear the suction noise coming from where I think the diaphragm base connects to the main body, so hopefully its that gasket. But tonight will try doing the kill bleed test. And once the gaskets are replaced I wil hook the vacuum pump to the center tee and see how that works and also test the vacuum hoses.

You gotta have kill bleeds, they prevent the secondaries from opening too soon but, they also act to help pull them open once there's flow through the Venturi. That's why you can't just pull a vacuum and have them open. Size dictates how they work.

 

[440beep]

Here's one of the guilty gaskets

 

[440beep]

Now this all makes sense. I found a Six Pack article I stashed away with all my other Six Pack paperwork called "Installation and Tuning of the Six Pack Induction System" published in Jan 92 of Chrysler Power and it discusses the air bleed function on the secondaries very well. Now I understand Hemi what you were telling me to do.

Here's a question on the air bleeds, I see that Holley makes a ton of different size screw in air bleeds for the 4150 HP and 4500 Dominator carbs. Will these work on the Six Pack carbs? Guess I only have to thread the carbs for the screw in air bleeds.

You gotta have kill bleeds, they prevent the secondaries from opening too soon but, they also act to help pull them open once there's flow through the Venturi. That's why you can't just pull a vacuum and have them open. Size dictates how they work.

 

[68 HEMI GTS]

You


You gotta have kill bleeds, they prevent the secondaries from opening too soon but, they also act to help pull them open once there's flow through the Venturi. That's why you can't just pull a vacuum and have them open.

Now this all makes sense. I found a Six Pack article I stashed away with all my other Six Pack paperwork called "Installation and Tuning of the Six Pack Induction System" published in Jan 92 of Chrysler Power and it discusses the air bleed function on the secondaries very well. Now I understand Hemi what you were telling me to do.

Here's a question on the air bleeds, I see that Holley makes a ton of different size screw in air bleeds for the 4150 HP and 4500 Dominator carbs. Will these work on the Six Pack carbs? Guess I only have to thread the carbs for the screw in air bleeds.

your not going to want to mess with the air bleeds. better left alone unless your really a knowledgeable tuner. just make sure they are clear and open. now the outboard metering plates may need drilled out a bit depending on the combo.

 

[383man]

These guys are telling you right. But the vacum kill bleed for the secondaries or end carbs is not the type that has screw in bleed jets. You may be mixing up the high and idle speed air bleeds with the vacum secondary kill bleed. That secondary kill bleed is down in the venturi because is uses venturi vacum to help the secondaries open once they open far enough but it bleeds off vacum until the secondaries open far enough to start using the venturi vacum from in the venturi area. Its a small hole and I see no way you could drill it. I think you may be thinking of the idle and high speed bleeds in the top of the carb airhorn as many of these with billet metering blocks have screw in jets in them. But try pulling vacum on them with your finger over the kill bleed hole and see how that works. Ron

 

[440+6]

These guys are telling you right. But the vacum kill bleed for the secondaries or end carbs is not the type that has screw in bleed jets. You may be mixing up the high and idle speed air bleeds with the vacum secondary kill bleed. That secondary kill bleed is down in the venturi because is uses venturi vacum to help the secondaries open once they open far enough but it bleeds off vacum until the secondaries open far enough to start using the venturi vacum from in the venturi area. Its a small hole and I see no way you could drill it. I think you may be thinking of the idle and high speed bleeds in the top of the carb airhorn as many of these with billet metering blocks have screw in jets in them. But try pulling vacum on them with your finger over the kill bleed hole and see how that works. Ron

Just for your info, people do drill and tap the kill bleeds ( you remove the diaphragm and drill through there) then use brass plug with holes drilled in them for their application. The first mods where to pound a piece of lead shot in there to block it off compleatly so the secondaries would open almost instantly.