# 67-69 400 Quadrajet Secondary Restriction



## GTOJoe1968 (Feb 19, 2018)

This question is pertaining to a 67 Firebird 400 Quadrajet, but I've read a lot of info here on the subject by knowledgeable posters so I thought I'd post here (since GTOs use same carb but without restrictor). As I said, I’ve read a lot about this alleged restriction in this forum and also some other forums and am trying to get an accurate understanding of how to identify and remove this “restrictor” if it in fact does exist on my 67 Firebird 400. Instead of rehashing what’s already been stated I just collected and pasted sections from previous conversations on the subject below.

_“The Firebird carbs, usually on the higher HP engines, had a "limiter" on the secondary. GTO carbs did not have them.
The 1967-1970 Q-jets rated at 650 CFM has a *secondary air-valve lock-out lever that prevents the air-valve from opening completely*. You can *bend the lever upwards or snip it off with a pair of dikes* and make your 650 CFM Q-jet into a 750 CFM Q-jet and add 100 CFM at WOT. That little lock-out lever functions like a governor or rev-limiter.

For example, GM included that feature on the 650 CFM Q-jets used on the 1967-1970 Pontiac 400 CI engines so they could use the same Q-jet on 1967-1970 regular production 400 CI engines rated at 325 HP. That lever restricts the opening of the secondary air valve to 90% in order to maintain the General Motors front office horsepower requirement of 10 lb. per 1 HP, for insurance purposes.

For example: 1967-1969 Firebird 400 CI engine, rated at 325 HP and 3250 lb. curb weight. That engine was identical to a 1968-1969 GTO 400 CI engine, rated at 350 HP and 3506 lb. curb weight. The Q-jet on the 1968-1969 GTO did not receive the Q-jet with the Secondary Air Valve Lock Out lever.

If I can remember correctly, you could not just remove the "Lock Out Lever" because a portion of the part also served as a washer for the Secondary Air Valve shaft. That is why it was necessary to bend or snip off the portion of the lever that prevents full opening of the Secondary Air Valve, for an additional 25 HP at WOT”_

Here is also a Jim Mattison quote from Hemmings.com, founder and owner of Pontiac Historical Services: _“The only difference, according to Jim Mattison, founder and owner of Pontiac Historical Services, was a slightly different throttle linkage that prevented the Rochester Quadrajet's secondaries from opening more than 90 percent. "It just needed to be bent a little bit to open the secondaries up all the way," Jim told us. "It took all of 20 seconds." With the new throttle linkage, Pontiac could officially rate the Firebird 400's engine at 325 hp at 4,800 rpm, and 410 lb-ft of torque at 3,600 rpm.”_

Okay so pic below is my original 67 400 quadrajet with an arrow pointing to what it sounds like is described and also illustrated and described in Cliff Ruggles book. I have also attached Cliff’s pic and description. Is where I have my arrow pointed to what all this discussion is about? If I bend this so that it doesn’t hit the stop at the top of the carb does that give me the extra 25 HP discussed?


----------



## BearGFR (Aug 25, 2008)

Some QJets as I understand it had this limiter on the air valve, others may have had a similar limiter on the secondary throttle blades. Since you have Cliff's book, go to the section on how to tune/adjust your carb and verify that both your air valve and your throttle blades can open to the "right" orientation for WOT. You should be good.

Bear


----------



## GTOJoe1968 (Feb 19, 2018)

BearGFR said:


> Some QJets as I understand it had this limiter on the air valve, others may have had a similar limiter on the secondary throttle blades. Since you have Cliff's book, go to the section on how to tune/adjust your carb and verify that both your air valve and your throttle blades can open to the "right" orientation for WOT. You should be good.
> 
> Bear


I no longer have the book as I borrowed it, but I looked it through and through for all info I could on this and it has brought me to this point where there are still questions. This seems like something old school Pontiac heads may know and can confirm for me with my question and pics. BTW it appears my throttle blades open all the way, but it's really hard to tell.


----------



## BearGFR (Aug 25, 2008)

The book should be available still on Amazon


----------



## GTOJoe1968 (Feb 19, 2018)

BearGFR said:


> The book should be available still on Amazon


The exact info I'm looking for is not in the book. Hence why I posted here and provided details and illustrations to clarify my exact question, which is, "Is this what I bend"?


----------



## PontiacJim (Dec 29, 2012)

Yes, the Firebird's with the same "GTO" engines were limited to a HP/weight requirement as was the GTO. The Firebird being lighter, had the carb that would not fully open to provide a lower HP to meet corporate HP/weight requirements.

You have 2 different things going on here and may be why the confusion.

The *Secondary Lockout* is found on top of the carb and prevents the secondary air flap from opening when the choke is on. There is a roll pin that can be knocked out to remove this lock. If it gets sloppy, sometimes it will hang up. Picture shows the lock out and location.

The photo you posted, Cliff's book, is correct in showing the *Secondary Air Flap Stop*. This is what would be different on the Firebird Q-jet having the same GTO engine and used to limit airflow/CFM's and thus the lowered HP rating on the Firebird - I believe the carb is rated as 650 CFM due to this stop, but is the typical 750 CFM Q-jet. The air flap should open about vertical when fully opened. The stop keep the flap from fully opening. If your flap does not open near vertically, or a little less, then you can grind the linkage stop according to the book. Cliff then drills and taps a small hole above the linkage tang/stop that goes through the top cover and extends below the cover that can be used to create an adjustable flap setting. But, I would pass on this modification and grind the tang on the linkage until I got the below measurement, or there abouts.

The book states that with the secondary flap fully open, the maximum opening distance should be 1.270" as measured from the leading edge of the flap (it's front) to the edge of the rear of the opening in the air horn. The calipers will be at an angle in doing this measurement.


----------



## BearGFR (Aug 25, 2008)

GTOJoe1968 said:


> The exact info I'm looking for is not in the book. Hence why I posted here and provided details and illustrations to clarify my exact question, which is, "Is this what I bend"?


Beg to differ.

Secondary air valve adjustment/tuning: pages 107-111, beginning with the topic heading "Secondary Air Flaps, Shaft Hanger, and Metering Rods"

Specific example of how to modify the carb so that the secondary air valve open limit is easily adjustable: photo on page 107
(Hint: Unless the carb is modified so that the air valve open limit is adjustable, this limit is addressed by grinding, not by 'bending' anything.)

Specific mention of how some carbs had the limiter you mentioned: two photos on the bottom of page 37.

Good explanation of "the right way" to tune the secondary air valve opening rate - something you do to "take the bog" out of a QJet: Page 109-111 under the heading "Choke Pull-Offs".

Specific adjustment for air valve opening, from page 109:
"With the flaps fully open, measure the distance from the leading edge of the flaps back to the edge of the rear opening of the air horn. The maximum open distance should be 1.270 inches. This duplicates the angle used by Edelbrock for its "850" cfm carburetors. For most applications, 1.280 to 1.330 inches is a good starting point."

How to tell if your primary and secondary throttle blades open fully and what to do about it if they don't. Page 89 These you do adjust by bending parts of the linkage. 

Bear


----------



## PontiacJim (Dec 29, 2012)

GTOJoe1968 said:


> The exact info I'm looking for is not in the book. Hence why I posted here and provided details and illustrations to clarify my exact question, which is, "Is this what I bend"?



Read my post #6.


----------



## gto4ben (May 27, 2018)

GTOJoe1968, Cold you please measure your air valve lock out lever as shown in the photo below? if it's a true 67 FB q-jet, I'd like to compare the lock out lever length to my 67 GTO q-jets. The carbs' lock out lever part number appears to be the 7032746 for all so the factory modified the length at a higher assembly level. If you compare my photo with yours, you can directly see the GTO ones appear shorter if you zoom in.


----------



## GTOJoe1968 (Feb 19, 2018)

PontiacJim said:


> Read my post #6.


PontiacJim thank you very much. I checked and do not have the Secondary Lockout on top of the carb as your pic shows. I DO have the Secondary Air Flap Stop you mentioned and can can definitely confirm that this does in fact stop the flap at about 80-90%-ish, and the way you explain it is exactly what I'm looking for. So I'm going to go for it. One thing I want to be clear on though; Do you think its best to grind the stop (meaning the actual aluminum stop at top that is part of carb body), or the steel linkage itself that hits the stop (where my arrow is drawn)? I was thinking the linkage because if I f* it up it is easier to reverse  What do you think?


----------



## GTOJoe1968 (Feb 19, 2018)

gto4ben said:


> GTOJoe1968, Cold you please measure your air valve lock out lever as shown in the photo below? if it's a true 67 FB q-jet, I'd like to compare the lock out lever length to my 67 GTO q-jets. The carbs' lock out lever part number appears to be the 7032746 for all so the factory modified the length at a higher assembly level. If you compare my photo with yours, you can directly see the GTO ones appear shorter if you zoom in.
> View attachment 158008


Thanks GTO4BEN. Great suggestion. I will do this tomorrow when I get to my garage. So that pic is a 67 GTO Q-Jet?


----------



## PontiacJim (Dec 29, 2012)

GTOJoe1968 said:


> PontiacJim thank you very much. I checked and do not have the Secondary Lockout on top of the carb as your pic shows. I DO have the Secondary Air Flap Stop you mentioned and can can definitely confirm that this does in fact stop the flap at about 80-90%-ish, and the way you explain it is exactly what I'm looking for. So I'm going to go for it. One thing I want to be clear on though; Do you think its best to grind the stop (meaning the actual aluminum stop at top that is part of carb body), or the steel linkage itself that hits the stop (where my arrow is drawn)? I was thinking the linkage because if I f* it up it is easier to reverse  What do you think?


I an not that versed on specific years/changes etc. on the Q-jets, but I believe not all have the secondary flap lock-out. I recall in my past that some did and I removed them and others did not, so I don't know where the difference lies.

I would not grind on the carb top/aluminum. I would grind away on the tab on the linkage piece for the reason you stated. If you messed it up, which I don't think you will, you can always get another linkage or tack weld a tack to it and grind as needed.

I would measure/take a photo of that tang just for personal reference and it may be helpful to someone else on the forum if you post the photo and the measurements. In Cliff's book, the "typical" stop looks almost flat, no real stick out to prevent the air flap from opening as it should. So I would grind a little at a time and used the air flap measurement given to get where you need to be.

With all that extra HP unleashed, you may want to install additional bolts to hold your seat down as that extra power may put you in that seat hard enough to rip it right out of the floor. 😆


----------



## gto4ben (May 27, 2018)

GTOJoe1968 said:


> Thanks GTO4BEN. Great suggestion. I will do this tomorrow when I get to my garage. So that pic is a 67 GTO Q-Jet?


Yes.


----------



## GTOJoe1968 (Feb 19, 2018)

Okay PontiacJim and GTO4Ben: So I took measurements and pics of fully opened secondary air flaps. Not looking good for me as I'm now thinking there is no 25hp out there for me to grab, but would like your thoughts. First pic is of the air valve lock out lever, which looks the same measurement as GTO4Ben's 67 GTO. 2nd pic is measurement of the stop. GTO4Ben if you could please measure you's as well that be great, although yours look same size as mine. 3rd is pic of fully opned secondary air flaps. GTO4Ben same thing if you could take a look at yours fully opened and let me know if it looks the same. I'm guessing mine is 90%, but that may be normal for GTO as well I'm thinking.


----------



## BearGFR (Aug 25, 2008)

Measure from the leading edge of the air valve flap, with it held fully open, to the back of the opening in the air-horn. This distance should be no less than 1.270". Between 1.280 and 1.330 is ok.









If it's not at least 1.270, then you have two options.
1) Grind this tab until it is.









2) Grind that tab completely off, then drill and tap a hole "just above" it and insert a screw that you can use to adjust how far the air-valve can open.









Don't alter/bend the linkage on the "choke pull-off" (the name doesn't match what it does). 

What it actually does, is control the opening rate of that "big barn door" secondary air valve. Here's how it works.

That diaphragm is connected to engine vacuum, such that when vacuum is present it pulls the linkage "to the front" and holds the secondary air valve shut. At wide open throttle, when manifold vacuum (essentially) goes to zero, a calibrated orifice in the diaphragm allows vacuum to "bleed off", relaxing the linkage, thus allowing the secondary air valve to open. (This is why you can't get the secondary air valve to open just by opening the the throttle with the car sitting in Park/Neutral. With no load, you can't get vacuum to drop enough to allow it.) 

The rate at which the vacuum bleeds off controls how quickly the air-valve can open. You don't want it to just "snap" open because what that would do would be to dump a huge gulp of air into the engine with no fuel to go with it - and you'd get a huge bog, just like what happens when your primary accelerator pump isn't delivering enough fuel. Instead you want that valve to open at a rate that's balanced with how quickly your secondary metering circuits are able to start feeding fuel. Many QJet "trick of the month club" members will tell you that you use the spring tension on the secondary air valve to control that. That's simply the wrong way to do it because enough spring tension to "work" is also enough tension to hinder the valve from fully opening, and/or cause it to bind. You want that spring just "barely" tight enough to reliably pull the valve shut with the engine off - and no tighter. To tune for max performance, you want to shoot for the 'fastest' air valve opening rate your engine will tolerate without creating a bog. There are different way to do that, but all of them boil down to "tuning" the orifice in the diaphragm that allows vacuum to bleed off at WOT.

The way I did mine, was to cut the hose to the diaphragm between it and the carb body, creating a spot where it needed to be 'spliced' back together. Then I drilled out the restriction in the diaphragm itself, making it way too big, and allowed the air valve to open way too fast. Next thing I did was to cut several short pieces of copper tubing that fit snug inside the vacuum hose, and completely plugged them with epoxy. After that I used tiny wire drills of different sizes to drill holes in the epoxy in each one of them - making a set of orifices all with different size holes in them. Then, I started with the smallest orifice I'd made, inserted it where I'd cut the vacuum line, then "bog tested" the car working my way up to progressively larger holes until I found the one that created a bog. The next smaller size was then the right one for my car.

Bear


----------



## PontiacJim (Dec 29, 2012)

BearGFR said:


> Measure from the leading edge of the air valve flap, with it held fully open, to the back of the opening in the air-horn. This distance should be no less than 1.270". Between 1.280 and 1.330 is ok.
> View attachment 158026
> 
> 
> ...


Good photos, but I believe your first picture is incorrect, "leading edge of the air valve flap, with it held fully open, to the *back *of the opening in the air-horn."

You show the measurement going to the front of the air-horn.


----------



## PontiacJim (Dec 29, 2012)

GTOJoe1968 said:


> Okay PontiacJim and GTO4Ben: So I took measurements and pics of fully opened secondary air flaps. Not looking good for me as I'm now thinking there is no 25hp out there for me to grab, but would like your thoughts. First pic is of the air valve lock out lever, which looks the same measurement as GTO4Ben's 67 GTO. 2nd pic is measurement of the stop. GTO4Ben if you could please measure you's as well that be great, although yours look same size as mine. 3rd is pic of fully opned secondary air flaps. GTO4Ben same thing if you could take a look at yours fully opened and let me know if it looks the same. I'm guessing mine is 90%, but that may be normal for GTO as well I'm thinking.


Pulled a pair of my Q-jets, one is 60's Pontiac and other early 70's Chevy.

1st pic shows the air flap lock out on the Pontiac carb.

2nd pic is the Pontiac carb fully open air flap. The lower, larger half, of the air flap is indeed angled. The smaller top section is more vertical. This air flap has the cut-outs to get fuel moving just before the flap opens - like a venturi affect.

3rd pic is a early 70's Chevy carb - no air flap lock out. Same deal. Slight angle on the larger section down in the carb and vertical on the upper section.

I also looked at the tang stop on the linkage piece. They were different in length BECAUSE the tops were slightly different in design. Not a big difference, but I could see the that Chevy top had a greater distance from the bottom of the aluminum casting where the stop hits to the bottom of the air horn that fits to the middle section/bowl of the carb - which would make sense as the tang/stop/linkage would need to be longer to compensate for the difference in design.


----------



## gto4ben (May 27, 2018)

BearGFR,
I tried to replicate your secondary flap measurement and I think your red arrow should be moved against the primary back wall. My measurement was 1-18/64" (1.281") for a stock fully opened air valve.
GTOJoe1968,
I added 0.020" to my lock out lever 0.355" using a feeler gauge to match your lockout lever measurement of 0.37". The result was an air flap opening of 1-14/64" (1.219).
The lock out flange thickness measured 0.228", comparable to what you measured.


----------



## GTOJoe1968 (Feb 19, 2018)

gto4ben said:


> BearGFR,
> I tried to replicate your secondary flap measurement and I think your red arrow should be moved against the primary back wall. My measurement was 1-18/64" (1.281") for a stock fully opened air valve.
> GTOJoe1968,
> I added 0.020" to my lock out lever 0.355" using a feeler gauge to match your lockout lever measurement of 0.37". The result was an air flap opening of 1-14/64" (1.219).
> ...


Thanks gto4ben. I will measure this shortly. What is your measurement without the feeler gauge on the lockout lever?


----------



## GTOJoe1968 (Feb 19, 2018)

GTOJoe1968 said:


> Thanks gto4ben. I will measure this shortly. What is your measurement without the feeler gauge on the lockout lever?


Sorry gto4ben, after re-reading I see you did do that and got measurement of 1.281.


----------



## GTOJoe1968 (Feb 19, 2018)

Okay now this is getting interesting. My measurement is 1 3/16 which is 1.1875. This is well short of the recommended minimum of 1.280 posted by Bear. Based on all this data I'm thinking even that smallest of differences in size of the lock out lever (Ben's .355 to my .37) is multiplied fairly significantly in the opening of the air flaps. Based on Ben's feeler gauge test where he added .020 to the lock out lever it appears the impact on the air flap opening is about x3 that addition (.062). So based on this math if I grind .02 off the lock out lever that should put my opening at about 1.2495, which is still a little short of 1.280. If I go .03 that should put me at about 1.2805 which would be right about where I need to be. So moving forward with formulating my plan I figure I'll grind off a little at a time until I get to about that 1.2805ish opening. So questions are 1- Does anything appear f*d up with my plan or math? 2- It sounds like a good idea for me to do this just to be within recommended Q-Jet specs, but we're still literally talking about 1/10th of an inch in that opening. Could this make that much of a difference in HP? I'm thinking....maybe. I mean the opening itself is about 1 inch so that IS 10% which kind of matches what is documented about the restriction (90% secondary opening restriction)


----------



## BearGFR (Aug 25, 2008)

My bad, and thanks to PJ for catching my mistake. I was wrong in how you take that measurement.
Here's a copy of the photo showing the correct procedure, scanned from Cliff's book.


----------



## BearGFR (Aug 25, 2008)

PontiacJim said:


> Good photos, but I believe your first picture is incorrect, "leading edge of the air valve flap, with it held fully open, to the *back *of the opening in the air-horn."
> 
> You show the measurement going to the front of the air-horn.


Correct! My bad - I've fixed my post with an updated photo.


----------



## GTOJoe1968 (Feb 19, 2018)

BearGFR said:


> My bad, and thanks to PJ for catching my mistake. I was wrong in how you take that measurement.
> Here's a copy of the photo showing the correct procedure, scanned from Cliff's book.
> 
> View attachment 158072


Okay so its difficult, for me anyway, to tell by that picture and description what exactly is being measured (since I'm not sure what "opening of the airhorn" is specifically referring to). So the easiest way for me to understand is to ask is this the same measurement GTO4BEN and I have taken that we discussed? See GTO4BEN's re-attached pic below as this is the measurement him and I have done. To be clear, I don't mean measurement result, I mean are we measuring the same points as your pic.


----------



## BearGFR (Aug 25, 2008)

Yeah, that's the wrong measurement. Instead measure from the BACK side of the air valve to the BACK of the secondary opening. I apologize for getting it wrong originally.

Like so:


----------



## GTOJoe1968 (Feb 19, 2018)

BearGFR said:


> Yeah, that's the wrong measurement. Instead measure from the BACK side of the air valve to the BACK of the secondary opening. I apologize for getting it wrong originally.
> 
> Like so:
> View attachment 158075


Okay, but that is for 850CFM. Is measurement same for 750 CFM? Regardless, one thing that is pretty clear to me at this point is that GTO4BEN's 67 GTO's factory 750 CFM Q-Jet secondary flaps open more than my 67 Firebird 400's factory 750 CFM Q-Jet secondary flaps.


----------



## PontiacJim (Dec 29, 2012)

GTOJoe1968 said:


> Okay, but that is for 850CFM. Is measurement same for 750 CFM? Regardless, one thing that is pretty clear to me at this point is that GTO4BEN's 67 GTO's factory 750 CFM Q-Jet secondary flaps open more than my 67 Firebird 400's factory 750 CFM Q-Jet secondary flaps.


I don't know of any factory 850CFM carbs - 750CFM and the later 800CFM. Maybe aftermarket Edelbrock?

Ben is measuring from the front of the airhorn, not the back, so disregard the measurement. *BearGFR* corrected his photo and provided the one from Cliff Ruggles book - that is the way to measure.

If you look down at the flap with it open, you will note with the flap wide open that the smaller section above the airhorn is not vertical to the larger section down in the carb - by design. When I looked at my carbs, if the top is vertical, the lower section is still at a slight angle. If I were to make the lower section vertical, the upper section would no longer be vertical and actually over center.

The air flap most likely has a slight tilt to maintain air/fuel velocity. If you go over-center on the smaller top section, you will most likely disrupt air flow and encounter other problems - my opinion.

If you grind, just make sure the small section of the flap is not over-center and if not, do as you mentioned to get the book measurement as long as not over-centering the smaller flap section that sticks above the airhorn.


----------



## gto4ben (May 27, 2018)

Three times the charm. It's tough to get an accurate measurement edge to edge with calipers so I used a steel ruler and magnets to hold them in place.

If measured diagonally:
1-21/64" (1.328") for the GTO
1-24/64" (1.375") for the GTO w/0.020 on the lockout lever.

If measured parallel to the air horn:
1-11/64" (1.171") for the GTO
1-17/64" (1.265") for the GTO w/0.020" on the lockout lever as shown

The opening looks smaller for the GTO carb because the measurement decreases with more opening wrt back wall.



























Regardless how the opening is measured, I was interested in the differences from the factory stock secondary openings between 1967 GTO and 1967 Firebird Q-jets.

GTOJoe1968, not to deviate from the topic but did you ever disassemble your carb for a rebuild? One very unusual feature is the original power piston spring 7002071. It's initial use was in 1932-49 Single Barrel Rochester B and BC carbs. I'd like to confirm if the Firebirds got that spring. Rochester parts' list says they did.


----------



## GTOJoe1968 (Feb 19, 2018)

gto4ben said:


> Three times the charm. It's tough to get an accurate measurement edge to edge with calipers so I used a steel ruler and magnets to hold them in place.
> 
> If measured diagonally:
> 1-21/64" (1.328") for the GTO
> ...


So yeah result is pretty much in line with our previous tests. My opening is 1.4375 diagonal, which means smaller than GTO. Anyone know if Cliffs measurement recommendation of 1.270-1.330 is diagonal or straight? Can't tell by pic.


----------



## PontiacJim (Dec 29, 2012)

GTOJoe1968 said:


> So yeah result is pretty much in line with our previous tests. My opening is 1.4375 diagonal, which means smaller than GTO. Anyone know if Cliffs measurement recommendation of 1.270-1.330 is diagonal or straight? Can't tell by pic.


From my Post #6:

The book states that with the secondary flap fully open, the maximum opening distance should be 1.270" as measured from the leading edge of the flap (it's front) to the edge of the rear of the opening in the air horn. *The calipers will be at an angle in doing this measurement. *


----------



## BearGFR (Aug 25, 2008)

GTOJoe1968 said:


> Okay, but that is for 850CFM. Is measurement same for 750 CFM? Regardless, one thing that is pretty clear to me at this point is that GTO4BEN's 67 GTO's factory 750 CFM Q-Jet secondary flaps open more than my 67 Firebird 400's factory 750 CFM Q-Jet secondary flaps.


CFM rating of the carb doesn't matter. Keep in mind how the air valve works. The only force that causes it to open is engine demand/vacuum - i.e. - how 'hard' the engine is pulling. That's one of the design points that made the QJet so versatile and allowed it to work well on everything from the Pontiac Sprint-6 to the big GM V8's. That air valve made it into a variable CFM carb and was quite innovative. Because of how it worked, the air flow velocity through the secondaries was kept high enough to make the secondary metering circuits work well.

Bear


----------



## GTOJoe1968 (Feb 19, 2018)

Bear, Ben, Jim. Thank you very much for your help. It's obvious you guys put a lot of thought and time into your responses and it is very much appreciated. My plan is to grind away today and will let you know results. I will stop when I get to about 1.320, that way I grind as little as possible, but still within recommended parameters.

GTO4Ben- Regarding your question about disassembling my carb. I have not. I have only had this car about 3 months and the previous owner rebuilt the carb himself. I am still in touch with him and will ask if he knows about the power piston spring 7002071. It does seem like a long shot, but he is a very knowledgeable Pontiac guy and may have taken note. I'll let you know his response.

Joe


----------



## GTOJoe1968 (Feb 19, 2018)

Okay verdict is in. Although I do not have the equipment to literally measure HP, I would say it worked. Definitely has a little more jump to it when you suddenly floor it while cruising and let the kick-down down shift. Definitely made a difference!


----------



## PontiacJim (Dec 29, 2012)

GTOJoe1968 said:


> Okay verdict is in. Although I do not have the equipment to literally measure HP, I would say it worked. Definitely has a little more jump to it when you suddenly floor it while cruising and let the kick-down down shift. Definitely made a difference!


Excellent! The Q-jet is a great carb once set-up and adjusted. My personal choice is a Q-jet on a spreadbore intake and then the AFB for dual quads/square bore intake manifolds.

Have the new design AVS2, which Army also uses, which is what seems to be an upgrade on the AFB with better booster atomization and an adjustable secondary air flap.


----------



## GTOJoe1968 (Feb 19, 2018)

gto4ben said:


> Three times the charm. It's tough to get an accurate measurement edge to edge with calipers so I used a steel ruler and magnets to hold them in place.
> 
> If measured diagonally:
> 1-21/64" (1.328") for the GTO
> ...


Hi gto4ben. Wanted to let you know I didn't forget your question. His response was that the original spring was already replaced when he rebuilt it. Here is his full response: "The carburetor had been rebuilt once before so it didn’t have the original power piston or spring. I used parts from Cliffs High Performance for the rebuild. I spoke with him a couple of times by phone when I was rebuilding it. IMO their is no one on the planet with more Quadrajet knowledge than Cliff. He loves to talk also. If you want your question answered you should call him. He also has a Website with a forum that is pretty interesting"


----------



## gto4ben (May 27, 2018)

GTOJoe1968 said:


> Hi gto4ben. Wanted to let you know I didn't forget your question. His response was that the original spring was already replaced when he rebuilt it. Here is his full response: "The carburetor had been rebuilt once before so it didn’t have the original power piston or spring. I used parts from Cliffs High Performance for the rebuild. I spoke with him a couple of times by phone when I was rebuilding it. IMO their is no one on the planet with more Quadrajet knowledge than Cliff. He loves to talk also. If you want your question answered you should call him. He also has a Website with a forum that is pretty interesting"


Thanks!


----------

