# Secondary adjustment auto vs manual



## RMTZ67 (Mar 12, 2011)

I was reading a post on a forum about the difference in settings on the secondary flap on a automatic vs manual. The person mention how he believed that a manual trans needs a tighter setting on the flap and a one second vacuum can on it.I never knew they had such a thing. But I guess that's why they have carburetors for manual vs auto. I believe mine is a (even # carb = auto). What his summarization was that a manual car will stumble at wot because at shift the flap should close quickly prior to the shift and reacceleration...hence the one second can. Anyone hear of this theory? Assuming I have it correct.


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## BearGFR (Aug 25, 2008)

Opening rate is controlled by the diaphragm, not spring tension. 

Bear


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## RMTZ67 (Mar 12, 2011)

BearGFR said:


> Opening rate is controlled by the diaphragm, not spring tension.
> 
> Bear


So the diaphragm is what I was calling the can. He seemed to suggest that when you let off the accelerator to shift, that it should close quickly prior to the next shift and acceleration to prevent the bog in an a manual shift car. Hence the 1 second can (diaphragm). Is that the difference in manual and auto carbs? I was in the garage tryin to get my secondaries to open up like in this video and it would not. And I went pretty hard on the accelerator.


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## BearGFR (Aug 25, 2008)

That doesn't make sense to me. If the engine is already at rpm and at wot, having the airvalve close would be undesirable. Its main function is to ensure to allow fuel flow to "catch up" to air flow at the moment you first stand on it and open up those huge mechanical secondary throttle plates. Once everything has equalized and air flow through the secondaries has been well established, it doesn't seem like you'd want anything to impede that flow.

Bear


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## RMTZ67 (Mar 12, 2011)

BearGFR said:


> That doesn't make sense to me. If the engine is already at rpm and at wot, having the airvalve close would be undesirable. Its main function is to ensure to allow fuel flow to "catch up" to air flow at the moment you first stand on it and open up those huge mechanical secondary throttle plates. Once everything has equalized and air flow through the secondaries has been well established, it doesn't seem like you'd want anything to impede that flow.
> 
> Bear


hope I am not confusing the issue. I had a slight bog that I have been trying to address, But started wondering if my secondaries were opening because I didn't seem to here them over my exhaust. Then while making this post I came across that video and realized mine do not really open up like that while trying it in my garage. With the door open of course lol. The spring tension is mild..the lower secondaries open with the car off l, opening the accelerator and looking down the carb. What else would cause them not to open as in the video standing still and hitting the accelerator?


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## AZTempest (Jun 11, 2019)

He also has videos to address the bog.


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## integrity6987 (May 10, 2017)

In cliff's book - he suggests experimenting with different (very small e.g .022" max) orifices in the vacuum tube between the carb source and choke pull-off diaphragm.


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## PontiacJim (Dec 29, 2012)

RMTZ67 said:


> hope I am not confusing the issue. I had a slight bog that I have been trying to address, But started wondering if my secondaries were opening because I didn't seem to here them over my exhaust. Then while making this post I came across that video and realized mine do not really open up like that while trying it in my garage. With the door open of course lol. The spring tension is mild..the lower secondaries open with the car off l, opening the accelerator and looking down the carb. What else would cause them not to open as in the video standing still and hitting the accelerator?


The secondaries should pop open as in the video when you open the carb fast/hard - just as he did.

Do they open at all? With engine off, you should be able to push the secondary air flap open with your finger. There will be some resistance, but not a lot, from the spring that holds the flap closed - there should be no vacuum whatseover with engine off, so the spring wrap is the only thing holding it closed. Check this for operation and that it fully opens.

Some Q-jets have a "lock" that keeps the air flap closed when the choke is on. See Pic #1. If it is not functioning, maybe just disconnected, or flopping around, the air flap won't open. I always remove these if the carb has it. It will be right behind the primaries on top, it'll look like a kinda dog leg, and has a flat head screw coming in from the side and you just unscrew the screw and remove the lock.

The vacuum can holds vacuum which aides in closing the secondary air flap via a linkage rod. It can be fine tuned in that when the carb is kicked wide open, vacuum goes away, and this includes the vacuum can on the carb. As vacuum goes away, it allows the secondary air flap to open smoothly as the throttle blades are cracked open at the base of the carb, and create a transition that meters the air/fuel ratio going into the intake/engine.

If the vacuum can allows the secondary flap to pop open too quickly, then you get a poor transition of the air/fuel mixture and the engine sucks in more air that fuel and you get the bog UNTIL the fuel catches up with the airflow and things smooth out and the engine roars to life. If it were really too fast, you can even experience a backfire/pop from the carb, a big stumble, and then it'll pick up.

On the other hand, if the vacuum can is holding vacuum too long, it will hold the secondary flap closed longer than needed. You typically won't get a stumble because engine RPM's have risen and the flap will most likely open slowly anyway - so the air/fuel transition will be as it should be.

You can adjust the vacuum can's rate at which the vacuum exhausts from the can by creating "brass jets" of differing diameters and insert these in the hose connecting the vacuum can as a means of restricting vacuum flow - small brass tubes can be cut, drill sized, and swapped out to fine tune this feature. You can also drill the plastic nipple on the vacuum can to a few sizes up, but once opened up, you can't down size and that is where the different sized brass jets come into play.

You stumble can also be several other things - ie not enough fuel. There are different secondary rods that can richen up the secondary fuel mixture, or different hangers that hold the secondary rods - these can be had in different heights and raise the secondary rods higher out of the fuel well and faster to richen up the secondaries.

Can you adjust the secondary air flap using just the spring adjustment? YES. I used to do this with my Q-jets and remove the vacuum can. It can be trial and error until you find the best point at which the spring tension allows a smooth transition versus stumble. The spring tension generally will be a little on the tight side of adjustment, but it must not be too tight where the air flap won't fully open.

Look down into the secondaries while holding the air flap open. Are they fully opening? You want then near verticle, BUT, not vertical. There should be a slight angle. This helps to pull the air/fuel mixture in. If vertical, it can disrupt flow. This can be adjusted. 

You can also read a little more here:









Quadrajet - Simple Power Adjustments


Thought I would share some thoughts on Quadrajet adjustments as I remember doing in the late 1970's/early 1980's when I had my GTO's and used to tinker on other Pontiacs - and learned from reading magazine articles and hands-on work seeing we did not have the great resources today found on the...




www.gtoforum.com


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## RMTZ67 (Mar 12, 2011)

integrity6987 said:


> In cliff's book - he suggests experimenting with different (very small e.g .022" max) orifices in the vacuum tube between the carb source and choke pull-off diaphragm.





PontiacJim said:


> The secondaries should pop open as in the video when you open the carb fast/hard - just as he did.
> 
> Do they open at all? With engine off, you should be able to push the secondary air flap open with your finger. There will be some resistance, but not a lot, from the spring that holds the flap closed - there should be no vacuum whatseover with engine off, so the spring wrap is the only thing holding it closed. Check this for operation and that it fully opens.
> 
> ...


So originally I started wanting to cure a slight bog that I have been having. Then came across the video with the trans am secondaries opening while in park ,running and hitting the throttle. I know mine dont do that because I posted this video on a prior thread in which you commented on a fluttering choke plate. With the car off I look down the carb at open throttle and the lower throttle plates are opening up. I loosened the tension on the upper flap slightly and it would still not operate as in the trans am video. So even tho it ran great with the slight bog, I have a feeling my secondaries have not been opening up.Just thought I couldn't hear them over my exhaust. This video is from y last post but I tried it again yesterday with even higher rpms and no change.. secondaries would not open any further.


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## PontiacJim (Dec 29, 2012)

Ok, so the flap is not stuck. So, the vacuum can could be holding the flap back, ie the vacuum is not exhausting fast enough, but should do so in a long gear pull.

The spring tension on the flap could still be tight.

Pull off and plug the vacuum line for the vacuum canister (choke pull off) on the carb. This will disable it and not hold the air flap back. Try that and see if that changes things. If so, the slow opening would indicate the vacuum can is slow to exhaust.

Here is from Cliff's website and he says drilling the nipple as in mentioned in his book seems to be incorrect. Click on the link even though "error occurred." Seems to still work.






An Error Has Occurred!


An Error Has Occurred!



cliffshighperformance.com





Here is a PDF that gives you all the info you need. Download it for keeping.



https://www.carburetor-parts.com/assets/manuals/quadrajet_carburetor_manual.pdf



Does your carb have the baffle plate in the secondary bores looking down into the carb. If rebuilt, sometimes left out, but they are important and can eliminate bog by speeding up air/fuel flow during the transition period. Look at page 17, Fig. 15, 16, & 17 "Secondary Baffle Plates." If your carb had these and they were not re-installed, you should see the slots in the side walls of the secondaries where they would slide into.


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## RMTZ67 (Mar 12, 2011)

PontiacJim said:


> Ok, so the flap is not stuck. So, the vacuum can could be holding the flap back, ie the vacuum is not exhausting fast enough, but should do so in a long gear pull.
> 
> The spring tension on the flap could still be tight.
> 
> ...


I do have the baffle plates. I went into the garage and disconnected the hose to the diaphragm and tried again and it opened a slight more than my video but not much more. Certainly not wide open like the trans am. I would say about 1/2 " to 3/4 and probably enough pedal to annoy the neighbors . When i tried to open the baffles,it took 3/4 of the accelerator before it began to open. I think I would have to blow my engine to do what the trans am did.


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## PontiacJim (Dec 29, 2012)

OK, so improvement. Leave the vacuum break off again. Loosen the air flap spring tension - small adjusting spring screw on side/allen setscrew underneath. Insert allen wrench, loosen allen wrench just enough where you can turn the spring tension screw. Loosen 1/2 turn, then snug/tighten the allen screw. PDF, Page 26, Fig. 42.

Push down on air flap before adjusting so you can get a feel for the pressure needed to open the flap. Then once adjusted, it should take less pressure to open the flap by hand. Then start it up, and give it a try and see what you have.


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## BearGFR (Aug 25, 2008)

RMTZ67 said:


> hope I am not confusing the issue. I had a slight bog that I have been trying to address, But started wondering if my secondaries were opening because I didn't seem to here them over my exhaust. Then while making this post I came across that video and realized mine do not really open up like that while trying it in my garage. With the door open of course lol. The spring tension is mild..the lower secondaries open with the car off l, opening the accelerator and looking down the carb. What else would cause them not to open as in the video standing still and hitting the accelerator?


You'll never see then open with the car sitting in neutral/park in your driveway, no matter what you do to the throttle. In order for the diaphragm to release, manifold vacuum has to go to near zero and stay there for at least several seconds. You can't make that happen with no load on the engine. 

Bear


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## RMTZ67 (Mar 12, 2011)

BearGFR said:


> You'll never see then open with the car sitting in neutral/park in your driveway, no matter what you do to the throttle. In order for the diaphragm to release, manifold vacuum has to go to near zero and stay there for at least several seconds. You can't make that happen with no load on the engine.
> 
> Bear


I am gonna run it w/o air cleaner against my better judgment, to see if I can hear them open before making any changes.


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## Jd70 (Jul 4, 2019)

I see a choke valve thats not open all the way when you were revving in the video. It only opened all the way during the rev up. It should be vertical when fully warmed. Solve that first. It could be causing the lockout to stop air valve from opening. There are specs and process for checking that in shop manual or in carb rebuild kit instructions.
Also I to don’t think you can getthe air valve to open much in neutral either,
JD


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## RMTZ67 (Mar 12, 2011)

What do you guys think of this?


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## 67ventwindow (Mar 3, 2020)

RMTZ67 said:


> What do you guys think of this?


I thought it was the 1980's, cigarette in the mouth playing with carbs. Isnt that what the vacuum can is suppose to give you that sec, delay so you can mash the pedal and then have the secondaries roll in?


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## RMTZ67 (Mar 12, 2011)

67ventwindow said:


> I thought it was the 1980's, cigarette in the mouth playing with carbs. Isnt that what the vacuum can is suppose to give you that sec, delay so you can mash the pedal and then have the secondaries roll in?


Ya lol, sort of entertaining. Like he recorded it back in the days and pulled it out of archives for youtube. Waaaaaaa lol. Does it work? maybe but I would like mine to work complete. Not sure mine is working correctly. I ran mine without the air cleaner to listen for the waaaaaaa but couldn't honestly tell you if they were opening. Tough to tell with my exhaust. Still trying to figure it out without buying a gopro and sticking it under the hood. I think I got my bog corrected by tightening up my secondary spring a bit. I rebuilt my motor but don't know squat about Qjets.


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