[bhill86]

A topic that’s been a little beat to death maybe but the secondary air flaps on my Qjet aren’t opening very far at WOT. I have some videos below. No sound due to it being taken with my borescope taped to my hood.

Car is a 77 T/A with a ‘69 400 and I think the carb is off of a 78 auto car. My car is a 4 speed if that matters.

In the one video you’ll notice the front choke pull off doesn’t fully release initially but later does and the flaps still only open partially so I’m a little stumped.

https://youtube.com/shorts/KX3yJDcP1ds?feature=share

https://youtube.com/shorts/kEavAa9LelU?feature=share

https://youtu.be/U1Nohbyz1Fg

I bought this carb 8-10 years ago and ordered parts for a rebuild from Cliff but I couldn’t tell you what I ordered at the time.

[steve25]

Well it’s really hard to tell for sure from that photo angle but it looks to me like there’s something on the passenger air valve side of the carb that is sitting on top of the forwards part of the secondary metering rod hanger that should not be there!
It looks like it’s clamping down and restricting the hanger and thus the air flaps from opening up more!

[bhill86]

You kind of lost me there as to what you are referring to. I’m not sure if I’m looking in the right place. I should’ve mentioned though I can open the air flaps by hand fully. There is a slight increase in resistance in the same general area as where the flaps stop but I’m not sure if it’s the cam (maybe old and no longer shaped correctly?) or something else.

I can pop off the shaker and air cleaner for better pictures after work tonight if needed.

[Joe's Garage]

It's the part in the red circle in the pic below. I think that's what steve25 is seeing in your video. It looks like yours is not correctly ABOVE the choke flap rod - it might have been reassembled wrong at some point.

It keeps the secondary valve from opening when the engine is cold. Once the choke is fully heated up, the linkage holds it up so the flaps are free to open. Typical smog crap.....

We always remove them - just use a small screwdriver to bend the lockout lever and widen it so it will come off.

Nothing negative happens except the air valve opens whenever you want it to open.

NEVERMIND - I just watched the third video and it's not the issue. Your carb doesn't have one......

There is also a lockout on the secondary butterflies that locks THEM from opening when the engine is cold - that can be sticking and should be disabled, too. Here's a link to a site with info about that lockout:
https://www.carburetor-blog.com/know...jet-secondary/

As a third thought, will the open completely, or at least further, if you disconnect the vacuum from the choke pulloff and drive it around the block? You don't even need the camera for that test - you'll hear it if they open up all the way.

[Formulas]

Do you get full throttle with the pedal?

Can you open the air valve fully manually?

On the passenger side video the dashpot isnt restrictive most of the time

I dont see that secondary lock out in his vid

[bhill86]

Originally Posted by Joe's Garage

There is also a lockout on the secondary butterflies that locks THEM from opening when the engine is cold - that can be sticking and should be disabled, too. Here's a link to a site with info about that lockout:
https://www.carburetor-blog.com/know...jet-secondary/

As a third thought, will the open completely, or at least further, if you disconnect the vacuum from the choke pulloff and drive it around the block? You don't even need the camera for that test - you'll hear it if they open up all the way.

I’ll have to double check the secondary butterfly lockout. I don’t believe I have one but I’m not positive.

As far as whether or not they’ll open without the front pull off I haven’t tested that specifically but if you notice in the 3rd video around the 20 second mark the pull off releases further than the air flaps open so I assumed that they (air flaps) would act no different without the front pull off disabled (or linkage removed). If you think I should still give it a try I can though.

[bhill86]

Do you get full throttle with the pedal? - yes but I can double check.

Can you open the air valve fully manually? - yes

[formula kid]

Just taking a shot here, what is the tension of the secondary air flap spring. If it is set to tight no matter how hard you hit the go fast pedal the secondary's will not open fully.

[bhill86]

Originally Posted by formula kid

Just taking a shot here, what is the tension of the secondary air flap spring. If it is set to tight no matter how hard you hit the go fast pedal the secondary's will not open fully.

Admittedly I don’t know what is “proper” but I did check the tension today and loosened it so the flaps started to open then tightened it to the point that the flaps just closed which ended up putting me about a quarter turn less than it had been but the videos posted above are after that adjustment and there isn’t much, if any difference from before that adjustment.

[74Grandville]

could be the engine doesn't need more then that at the given rpm or load. that is the beauty of a vacuum secondary carb. it will only use what it needs unless you are hitting a stop, or the choke pull off is too slow. just because the carb is 750/800cfm doesn't mean the engine will use all that capacity during normal driving.

that is the issue with a double pumper on the street, it will give the engine more air than it needs, so to compensate, it dumps a ton of fuel. works well in drag racing, but very inefficient for the street.


I would verify the butterflies open perpendicular to the base plate on full throttle. I would also check the full opening of the secondary vacuum flaps on a bench to ensure nothing is hanging them up. the other thing to keep in mind is the mixture. if the mixture is not right, the engine will not pull as much air. as a properly tuned one.

[unruhjonny]

I saw the image of the secondary lockout, and thought to myself "that's not right for a 1978 Quadrajet", so I looked at the videos;

The third video one was the best one.

You can see in the third video that the linkage from the vacuum takeoff is allowing the secondaries to open wider - but they don't.

That linkage is there to hold the secondary (upper) butterfly closed until loss of vacuum, and demand from engine both warrant them opening.

I would look at the set tension of the secondary (upper) butterflies.

I don't know precisely what the setting should be, but I can tell by feel if it's too tight, or if it's about right;
It should be tight enough that they snap close nicely, but not so tight that there is too much tension which would prevent them from opening in the first place - with the linkage not holding it closed, it should open very easily.

The spring for the upper butterfly is held by a slotted end screw which is turned by a small flat head screwdriver - it is visible from the side of the carb, just behind the linkage connector;
The tension on this screw is placed there by a small allen head screw which is tapped into the bottom of the airhorn.
You loosen the allen head screw, and if you don't have a flat head screw driver in place, the screw holing the spring will spin so that there is no spring tension set against it.

You should be able to very lightly press your finger against the rear of the upper butterfly and open them, then lifting your finger should set them back;
If insufficient tension is set, the butterfly may not close, or may seem to hang up not fully closed.

Hopefully this helps.

[BLUE TA]

hi guys, do you think the cam for the secondary rods is cracked and the air valve hangs on it? just a thought. BLUE TA

[74Grandville]

Originally Posted by BLUE TA

hi guys, do you think the cam for the secondary rods is cracked and the air valve hangs on it? just a thought. BLUE TA

you might be on to something here. second vid shows the cam and it may have warn a divot into it.

[Cliff R]

It doesn't appear that the secondary throttle plates are opening more than about 20 percent.

Make sure they are opening to a full 90 degrees at WOT.......

[bhill86]

Thanks for the replies. I did adjust the air flap spring tension and it appears to be set as you described.

As for the cam, I wondered the same but there doesn’t seem to actually be any place to catch or hang up however if I open them with my finger there does seem to be a slight increase in resistance in roughly the same position as when the flaps stop opening during WOT

As far as the secondary throttle blades not opening I thought they were but when you mentioned it I thought “how can he see that from the angles of my videos” but I assume you could see it on the third video from the passenger side right? The “T” on the end of the secondary throttle shaft I assume. And you’re right, that doesn’t seem to be opening very far. After work tonight I’ll check.

[Joe's Garage]

Yeah, your butterflies are only opening about 1/4 of the way that they should.

The linkage adjustment is on the driver's side of the baseplate.

Second thought is that you need to verify that the GASKET you are using is not blocking the secondaries from opening.

If I recall correctly, the late 70s intakes had the restricted secondary openings and about a 1/4" thick gasket.

If the gasket is too THIN, the blades might be hitting the intake and stopping.

The more I think about it, I'm leaning towards this being the problem.

Here's info about the linkage adjustments:

https://cliffshighperformance.com/si...p?topic=4299.0

https://www.carburetor-blog.com/know...jet-secondary/

You get them adjusted so they open all the way and you will pick up a HUUUGE amount of power.

It will definitely make you smile.

Good luck.

[formula kid]

Looking at the third video again you can see where the secondary air flaps are trying to open. If you watch the vacuum break control is not releasing allowing the vacuum rod to get in the proper position. In order for the secondary flap to open the vacuum break rod has to be adjusted so when you jump on the car the vacuum pod can't hold rod forward. It looks as if there is an adjustment screw on that carb. I would look at the choke for your problem.

[bhill86]

Originally Posted by formula kid

Looking at the third video again you can see where the secondary air flaps are trying to open. If you watch the vacuum break control is not releasing allowing the vacuum rod to get in the proper position. In order for the secondary flap to open the vacuum break rod has to be adjusted so when you jump on the car the vacuum pod can't hold rod forward. It looks as if there is an adjustment screw on that carb. I would look at the choke for your problem.

Initially, yea you’re right. Without sound I know it’s hard to tell but the first 3 time they try to open is me at wot shifting through the gears. And yes, for whatever reason the vacuum break wasn’t releasing fully. After that though I think I was in 3rd gear and floored it and it the vacuum brake released more yet the flaps still didn’t open fully.

[Joe's Garage]

If you work the linkage from under the hood, with the engine OFF, and watch that little bar that goes thru the secondary throttle shaft on the passenger's side of the carb, check and see if the bar pivots any more than what is shown in the video #3.

If it doesn't open any more than in the video, the secondary butterflies are NOT opening very far and that's why the air valve doesn't open very far. Since it's dependent on airflow, it only opens as far as needed.

To check and see if the butterflies are hitting the intake due to a thin gasket, remove the four mounting bolts on the carb and lift it slightly (about 1/4") by sliding a couple of long screwdrivers in under it and on top of the gasket. Then work the linkage by hand, again watching that little bar thru the secondary throttle shaft.

If it now opens further, the gasket is letting the secondary throttle blades hit the intake manifold.

You don't need to undo all the fuel lines and vacuum hoses and such. Just get the carb lifted up 1/4" or so and see what happens.

[bhill86]

Ugh….I’m a bit embarrassed to say but I found my issue tonight I’m pretty sure. I don’t know how I never noticed but the reason the secondaries were only opening a slight bit is because the PRIMARIES were only opening part way BECAUSE my cruise control cable was hanging up on the aftermarket throttle cable bracket I have and preventing the primaries from opening. There wasn’t much difference in feel at the pedal once I fixed it (bending the bracket slightly) but it seems to have made all of the difference with the remainder of the primary travel and subsequently the secondaries opening completely.

I think when I opened the throttle by hand there was no hang up but via the peddle, there was enough difference to allow the hang up. We shall see tomorrow.

Thank you to everyone who responded. Sorry it ended up being something that should’ve been pretty obvious had I spent more time looking closer. I did learn from it though so that’s a plus.