Quadrajet specs help!
07-13-2016, 09:46 PM
#1
Instructor
Thread Starter
Quadrajet specs help!
My first posting as a new member- hopefully I don't screw this up...
I have been finding very useful info here for the past couple of years and hold a lot of respect for the people who offer their help.
I have owned a '68 L-36 since 1985 and have restored much of the car in the past couple of years. I needed a carb since my Holley needed major maintenance and decided to go with a Quadrajet clone to make it look more original and like the precision of the design overall.
People on this forum seemed to give the carb guy I used pretty positive remarks. After installation, carb kept falling flat on its face when getting into secondaries. Finally, he sent me AX rods which were supposed to be in the 7028209 according to Lars which helped quite a bit, but is still has a slight hesitation at WOT. The carb he sent is stamped 7029207 which I believe is from a '69 365 HP vette with manual transmission. He said it would be reconfigured to mimic or "clone" the 7028209, but the BG rods were the first thing I wondered about.
After going through ignition and timing, plugs, wires, etc, I finally pulled the top off the carb and found:
1) mismatched primary rods (2.40 length mixed with 2.47)
2) primary jet size .066 with .045 rod (before taper), should be 71/45
3) inlet seat size of .110 (Cliff Ruggles told me that would be too small)
I have a .030 bored over and a cam with 110 lobe centers so it's by no means radical. Newly rebuilt distributor with Breakerless SE unit. It pulls strong when I accelerate in the primaries but at about 3500 to 4000 rpm it starts to hesitate slightly, not really a stumble.
Idle is not rough, but not as smoothe as it should be, and the mixture screws don't have much effect on vacuum or idle quality. Vacuum flutters slightly +/- half an inch or so around 15 inches.
I can't find anywhere on line what all the specs of the 7028209 should really be, including bleed sizes, tube sizes, inlet seat size, etc. I have a lot of faith that Lars' paper is correct that it should use AX rods, and have the 71/45 primary jet/rod combo. Does anyone have access to this information? The carb guy is sending me new primary rods, a .130 seat, and .071 jets. This may do no good if the bleeds are not correct.
Sorry this is so long but I think all the info I included was pertinent.
Thanks for any input anyone has to offer!
I have been finding very useful info here for the past couple of years and hold a lot of respect for the people who offer their help.
I have owned a '68 L-36 since 1985 and have restored much of the car in the past couple of years. I needed a carb since my Holley needed major maintenance and decided to go with a Quadrajet clone to make it look more original and like the precision of the design overall.
People on this forum seemed to give the carb guy I used pretty positive remarks. After installation, carb kept falling flat on its face when getting into secondaries. Finally, he sent me AX rods which were supposed to be in the 7028209 according to Lars which helped quite a bit, but is still has a slight hesitation at WOT. The carb he sent is stamped 7029207 which I believe is from a '69 365 HP vette with manual transmission. He said it would be reconfigured to mimic or "clone" the 7028209, but the BG rods were the first thing I wondered about.
After going through ignition and timing, plugs, wires, etc, I finally pulled the top off the carb and found:
1) mismatched primary rods (2.40 length mixed with 2.47)
2) primary jet size .066 with .045 rod (before taper), should be 71/45
3) inlet seat size of .110 (Cliff Ruggles told me that would be too small)
I have a .030 bored over and a cam with 110 lobe centers so it's by no means radical. Newly rebuilt distributor with Breakerless SE unit. It pulls strong when I accelerate in the primaries but at about 3500 to 4000 rpm it starts to hesitate slightly, not really a stumble.
Idle is not rough, but not as smoothe as it should be, and the mixture screws don't have much effect on vacuum or idle quality. Vacuum flutters slightly +/- half an inch or so around 15 inches.
I can't find anywhere on line what all the specs of the 7028209 should really be, including bleed sizes, tube sizes, inlet seat size, etc. I have a lot of faith that Lars' paper is correct that it should use AX rods, and have the 71/45 primary jet/rod combo. Does anyone have access to this information? The carb guy is sending me new primary rods, a .130 seat, and .071 jets. This may do no good if the bleeds are not correct.
Sorry this is so long but I think all the info I included was pertinent.
Thanks for any input anyone has to offer!
07-14-2016, 12:20 PM
#2
I think you might benefit by getting a copy of Cliff Ruggles book on Quadrajets.
https://www.amazon.com/Rebuild-Modif.../dp/1932494189
Based on the book recommendations the .135 seat covers most street performance setups.
The book also has suggested sizes for the other components.
The 41/75 jet/rod is what Lars shows in his listing for the carb along with the AX rods.
Have you adjusted the tension on the secondary flap, starting point would be 1/2 to 3/4 of a turn?
have you adjusted the float level to .250?
https://www.amazon.com/Rebuild-Modif.../dp/1932494189
Based on the book recommendations the .135 seat covers most street performance setups.
The book also has suggested sizes for the other components.
The 41/75 jet/rod is what Lars shows in his listing for the carb along with the AX rods.
Have you adjusted the tension on the secondary flap, starting point would be 1/2 to 3/4 of a turn?
have you adjusted the float level to .250?
Last edited by MelWff; 07-14-2016 at 12:23 PM.
07-14-2016, 01:54 PM
#3
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After going through ignition and timing, plugs, wires, etc, I finally pulled the top off the carb and found:
1) mismatched primary rods (2.40 length mixed with 2.47)
2) primary jet size .066 with .045 rod (before taper), should be 71/45
3) inlet seat size of .110 (Cliff Ruggles told me that would be too small)
1) mismatched primary rods (2.40 length mixed with 2.47)
2) primary jet size .066 with .045 rod (before taper), should be 71/45
3) inlet seat size of .110 (Cliff Ruggles told me that would be too small)
Lars
07-14-2016, 02:04 PM
#4
Instructor
Thread Starter
Hi MelWff and thanks for helping out!
I have had Doug Roe's book since the early 90's and have consumed as much information as possible. I emailed Cliff and he said my seat was too small at .110 and carb builders often just throw in whatever they might have. After hearing good things about the guy I used in NJ, I had him build a clone that was supposed to have all correct insides. I was really disappointed when I discovered the wrong primary rods and primary jets, as well as the wrong secondary rods. I am now wondering if anything else may be incorrect.
I have the float adjusted at .3 (spec is .25 and Lars suggests .375 on this year for street) and I have played around with the secondary air valve at 1/8 intervals from 1/2 to 1 1/4 and it seems to work best right around the suggested 7/8.
Three questions would be then...
Do you think that if I have the .110 seat and the float adjusted a little lower than the .25 spec that it could be starving at high rpm?
Do you know if the air bleeds, idle air vents, transfer tubes, etc, are all the same on the '68 and '69 carbs for small blocks and big blocks?
Do you know if Ruggles' book has the actual specs for each carb by number, because Roe's book does not?
I have to give the guy some credit for at least working with me over the phone and sending me, hopefully, the correct parts.
Again, I really appreciate you taking the time to respond to my first post.
Kirk H
I have had Doug Roe's book since the early 90's and have consumed as much information as possible. I emailed Cliff and he said my seat was too small at .110 and carb builders often just throw in whatever they might have. After hearing good things about the guy I used in NJ, I had him build a clone that was supposed to have all correct insides. I was really disappointed when I discovered the wrong primary rods and primary jets, as well as the wrong secondary rods. I am now wondering if anything else may be incorrect.
I have the float adjusted at .3 (spec is .25 and Lars suggests .375 on this year for street) and I have played around with the secondary air valve at 1/8 intervals from 1/2 to 1 1/4 and it seems to work best right around the suggested 7/8.
Three questions would be then...
Do you think that if I have the .110 seat and the float adjusted a little lower than the .25 spec that it could be starving at high rpm?
Do you know if the air bleeds, idle air vents, transfer tubes, etc, are all the same on the '68 and '69 carbs for small blocks and big blocks?
Do you know if Ruggles' book has the actual specs for each carb by number, because Roe's book does not?
I have to give the guy some credit for at least working with me over the phone and sending me, hopefully, the correct parts.
Again, I really appreciate you taking the time to respond to my first post.
Kirk H
07-14-2016, 02:12 PM
#5
Instructor
Thread Starter
By the way, Lars did NOT build this carb- I wish he would have. I was under the impression he was out of the business. I have learned a ridiculous amount of information from his technical papers, and am very gracious that he has donated so much of this to the public.
Kirk H
Kirk H
07-14-2016, 11:55 PM
#6
Burning Brakes
Heres what I have. First pic is stuff you already know, second is adjustment specs from the big GM carb book. Unfortunately Ive never been able to find info on air bleeds but if the top plate on your carb is indeed from a 69 it should work pretty well for you.
If youd like, I can post pics of the figures referenced to in the second pic.
If youd like, I can post pics of the figures referenced to in the second pic.
07-15-2016, 12:49 AM
#7
Instructor
Thread Starter
Thanks Dugsgms74-
I was really hoping someone might know if I was doomed or not with having to have the whole thing redone. Jets, rods, and seats are easy but I did not want to have paid $600 for this to be COMPLETELY redone! You've given me a little bit of hope
Thanks
Kirk H
I was really hoping someone might know if I was doomed or not with having to have the whole thing redone. Jets, rods, and seats are easy but I did not want to have paid $600 for this to be COMPLETELY redone! You've given me a little bit of hope
Thanks
Kirk H
Last edited by Kirk H; 07-15-2016 at 12:51 AM.
07-15-2016, 04:26 AM
#8
Burning Brakes
Kirk, no problem. Just to add, I looked up the adjustment specs for the 7029207 and everything is the exact same as the 7028209 except the unloader adjustment which is .450 rather than .300.
While those two carbs have different part #s for all major parts(air horn, body and throttle plate) alot of the differences between them were configuration rather than calibration differences. For instance, pretty much all car big block Q-jets in 68 use the same air horn, body and throttle plate part #s for both STD and HP applications. Youre better off having a "matched set" of major parts than trying to make a 7029207 into a 7028209 by swapping major parts around. The only caveat is that the 7028209 uses a unique, 1 year only choke coil/choke arm set up that is nearly impossible to find but you can make it work by using a 69-up coil and rod.
Since you already have the carb, I'd go ahead and install all the correct parts for 7028209(jets,rods, power spring etc.) and set up EVERY adjustment to spec and see where you end up. You might be surprised how well it will works.
Good Luck, Doug
While those two carbs have different part #s for all major parts(air horn, body and throttle plate) alot of the differences between them were configuration rather than calibration differences. For instance, pretty much all car big block Q-jets in 68 use the same air horn, body and throttle plate part #s for both STD and HP applications. Youre better off having a "matched set" of major parts than trying to make a 7029207 into a 7028209 by swapping major parts around. The only caveat is that the 7028209 uses a unique, 1 year only choke coil/choke arm set up that is nearly impossible to find but you can make it work by using a 69-up coil and rod.
Since you already have the carb, I'd go ahead and install all the correct parts for 7028209(jets,rods, power spring etc.) and set up EVERY adjustment to spec and see where you end up. You might be surprised how well it will works.
Good Luck, Doug
Last edited by dugsgms74; 07-15-2016 at 04:43 AM.
07-15-2016, 10:47 AM
#9
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You cannot take one carb number and "create" another carb number simply by swapping jets and rods. That makes as much sense as taking the carb jetting specs from a Stromberg and putting those sized parts in a Holley because you want the Holley to run like a Stromberg on your '49 Cadillac.
The small block and big block carbs do not have the same air bleeds or IFR sizes, so you can't just swap jets/rods around. For a proper setup, jet the carb for it's original carb number. A carb doesn't "know" what engine its running on - it just senses airflow. The carb jetting needs to work with its other internal calibration - irrelevant of the engine you're putting it on. Once the carb is correctly set up for its carb number, you can then make minor tuning changes based on specific needs of your engine. But these should be fairly small changes from the carb's baseline spec. Any carb correctly set up to its base spec will run pretty darned good on just about any engine in the normal "performance street" range. This, of course, assumes that the carb's components are unaltered, correct, undamaged, and in normal, good working order (which I find in only about 50% of the cases anymore).
By the way, I do offer a carb "testing" service for a fee much lower than the rebuild and setup fee. If you want me to simply test your carb and give it an evaluation, I can do so. I can't test for actual transition into the secondaries under load, but I can often find issues that would cause the complaint condition through a thorough test, inspection, and teardown evaluation. E-Mail me for info.
Lars
V8FastCars@msn.com
The small block and big block carbs do not have the same air bleeds or IFR sizes, so you can't just swap jets/rods around. For a proper setup, jet the carb for it's original carb number. A carb doesn't "know" what engine its running on - it just senses airflow. The carb jetting needs to work with its other internal calibration - irrelevant of the engine you're putting it on. Once the carb is correctly set up for its carb number, you can then make minor tuning changes based on specific needs of your engine. But these should be fairly small changes from the carb's baseline spec. Any carb correctly set up to its base spec will run pretty darned good on just about any engine in the normal "performance street" range. This, of course, assumes that the carb's components are unaltered, correct, undamaged, and in normal, good working order (which I find in only about 50% of the cases anymore).
By the way, I do offer a carb "testing" service for a fee much lower than the rebuild and setup fee. If you want me to simply test your carb and give it an evaluation, I can do so. I can't test for actual transition into the secondaries under load, but I can often find issues that would cause the complaint condition through a thorough test, inspection, and teardown evaluation. E-Mail me for info.
Lars
V8FastCars@msn.com
Last edited by lars; 07-15-2016 at 10:48 AM.
07-15-2016, 01:20 PM
#10
Instructor
Thread Starter
[QUOTE]
The small block and big block carbs do not have the same air bleeds or IFR sizes, so you can't just swap jets/rods around. For a proper setup, jet the carb for it's original carb number. /QUOTE]
Thanks for chiming in here, Lars. You've definitely cleared up my question as to whether or not the idle bypass air, idle tubes, IAB's, etc would would be different. It would make sense that the difference in CID would create different demands. When the I spoke with the carb "clone" builder a few days ago about the incorrect parts I discovered, I also asked about these other items. He said all the bleeds, tubes, etc were all changed to match the 7028209, for what that's worth.
You said any carb set up to spec would run pretty good on a street engine... can the small block carb (7029207) be modified like he said if it's done correctly? Are there specs available on the orifice sizes so I can measure them myself with measuring rods or drills?
If not, I guess the easiest thing to do is to install the correct jets/rods, and seat when they show up and see how it works. If it still has trouble, I think I would like to take advantage of your testing service.
I recall reading in a post somewhere that you were not actively working on peoples carbs any more except except hard luck or pity cases. I don't think I'm quite there and I really enjoy troubleshooting thanks to your papers. While very informative, Doug Roe's book does not cover troubleshooting like you graciously have.
Many thanks again
Kirk H
The small block and big block carbs do not have the same air bleeds or IFR sizes, so you can't just swap jets/rods around. For a proper setup, jet the carb for it's original carb number. /QUOTE]
Thanks for chiming in here, Lars. You've definitely cleared up my question as to whether or not the idle bypass air, idle tubes, IAB's, etc would would be different. It would make sense that the difference in CID would create different demands. When the I spoke with the carb "clone" builder a few days ago about the incorrect parts I discovered, I also asked about these other items. He said all the bleeds, tubes, etc were all changed to match the 7028209, for what that's worth.
You said any carb set up to spec would run pretty good on a street engine... can the small block carb (7029207) be modified like he said if it's done correctly? Are there specs available on the orifice sizes so I can measure them myself with measuring rods or drills?
If not, I guess the easiest thing to do is to install the correct jets/rods, and seat when they show up and see how it works. If it still has trouble, I think I would like to take advantage of your testing service.
I recall reading in a post somewhere that you were not actively working on peoples carbs any more except except hard luck or pity cases. I don't think I'm quite there and I really enjoy troubleshooting thanks to your papers. While very informative, Doug Roe's book does not cover troubleshooting like you graciously have.
Many thanks again
Kirk H
07-15-2016, 05:51 PM
#11
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2. There are no published specs for the bleed and restrictor sizes, so if they've screwed with the metering parts, there is no way to establish what they've done nor any way to return the carb to a known baseline
3. As bad as they screwed up the simple stuff (i.e., jetting that was WAY out of spec, mismatched primary rod style, wrong primary rod sizes for the jet sizes, wrong secondary rods, etc., etc.,) I wouldn't put any credence in anything they told you about correctly sizing the bleeds and restrictors. I'll bet they don't even know what size those parts should be on either one of the carb numbers.
I'm afraid they may have created a very expensive doorstop for you. Find an unmolested carb and set it correctly without molesting the base configuration.
Lars
07-16-2016, 12:45 AM
#12
Instructor
Thread Starter
I think I see what you are now saying...
I installed the 72 jets (supposed to send 71) and correct 45B rods that he sent me today and it was ridiculously rich- turned idle screws in completely to get 15-16 vacuum but terrible response, rough idle and surge at cruise.
Then I read your last post-
So if I understand you (and your tuning paper) correctly, best thing to do is return carb to the jet/rod combo for its 7029207 specs (66/36 jet/rod) and and make minor tuning techniques, even though this is a small block carb sitting on a big block. By this I assume you mean experiment incrementally in 10% amounts, making sure to keep the cruise metering area constant with appropriate rods, as outlined in your tuning paper.
The carb actually performed pretty well with the 66/45 combo he had and pulled strong until it started to just slightly stumble at high rpm (4000+). It idled fairly smooth but had a slight fluttering vacuum around 15", maybe due to the 110 cam. Response with accelerator pump off was slight hesitation as well, so maybe it was close after all.
I don't think any bleeds or tubes were changed out so maybe this carb is salvageable. I'll see if the builder will send me incremental jets, rods and springs to play with and start with the 66/36 for this carb. He's worked with me so far and has offered to look the carb over again without any questions. I have not dragged his name through the mud on the forum because he may want a chance to make it right.
Again, thanks for you time- it is sincerely appreciated. If and when I do give up, may I email you about that testing service?
Kirk H
I installed the 72 jets (supposed to send 71) and correct 45B rods that he sent me today and it was ridiculously rich- turned idle screws in completely to get 15-16 vacuum but terrible response, rough idle and surge at cruise.
Then I read your last post-
So if I understand you (and your tuning paper) correctly, best thing to do is return carb to the jet/rod combo for its 7029207 specs (66/36 jet/rod) and and make minor tuning techniques, even though this is a small block carb sitting on a big block. By this I assume you mean experiment incrementally in 10% amounts, making sure to keep the cruise metering area constant with appropriate rods, as outlined in your tuning paper.
The carb actually performed pretty well with the 66/45 combo he had and pulled strong until it started to just slightly stumble at high rpm (4000+). It idled fairly smooth but had a slight fluttering vacuum around 15", maybe due to the 110 cam. Response with accelerator pump off was slight hesitation as well, so maybe it was close after all.
I don't think any bleeds or tubes were changed out so maybe this carb is salvageable. I'll see if the builder will send me incremental jets, rods and springs to play with and start with the 66/36 for this carb. He's worked with me so far and has offered to look the carb over again without any questions. I have not dragged his name through the mud on the forum because he may want a chance to make it right.
Again, thanks for you time- it is sincerely appreciated. If and when I do give up, may I email you about that testing service?
Kirk H
08-05-2016, 01:11 PM
#13
Instructor
Thread Starter
Finally fixed the issue!
Phillip Cancilla at Custom Rebuilt Carbs worked with me repeatedly to solve my issue. He sent me various rods and jets, bigger needle and seat, and a generous amount of phone time to help me figure out the issue. As it turns out, I could not get any of the changes to work correctly because my fuel pressure was too high. It was not high enough to spot any of the tell-tale signs of fuel seepage into the throttle bores or venturi, or shooting gas, but high enough to make the fuel level in the bowl too high while cruising. It was a brand new AC Delco 40727 for big blocks and was the same one I had used before with a Holley, but it was running at 8.5 psi- too much for the Quadrajet. I changed it out for an Airtex replacement which now runs at 6 psi and now the car performs great at WOT, with no sputtering or hesitation of any kind. Phillip had suggested checking my pressure first off, but since the car originally ran fine except at WOT with this pump on the new carb and saw no signs of high pressure, we moved on to re-jetting and needle and seat.
When the move from 66 to 68 jets showed wet gas on the plugs, he insisted I check the fuel pressure. Now I just need to pinpoint the rods using Lars' tuning technique. 45's were running a little rich (throttle flick response better with pump detatched) so I tried 47's. Slight surge at cruise so hopefully 46's will work perfectly.
Hopefully, this follow-up will help others... I have seen so many posts that never get fully resolved and always wonder what happened!
Phillip Cancilla at Custom Rebuilt Carbs worked with me repeatedly to solve my issue. He sent me various rods and jets, bigger needle and seat, and a generous amount of phone time to help me figure out the issue. As it turns out, I could not get any of the changes to work correctly because my fuel pressure was too high. It was not high enough to spot any of the tell-tale signs of fuel seepage into the throttle bores or venturi, or shooting gas, but high enough to make the fuel level in the bowl too high while cruising. It was a brand new AC Delco 40727 for big blocks and was the same one I had used before with a Holley, but it was running at 8.5 psi- too much for the Quadrajet. I changed it out for an Airtex replacement which now runs at 6 psi and now the car performs great at WOT, with no sputtering or hesitation of any kind. Phillip had suggested checking my pressure first off, but since the car originally ran fine except at WOT with this pump on the new carb and saw no signs of high pressure, we moved on to re-jetting and needle and seat.
When the move from 66 to 68 jets showed wet gas on the plugs, he insisted I check the fuel pressure. Now I just need to pinpoint the rods using Lars' tuning technique. 45's were running a little rich (throttle flick response better with pump detatched) so I tried 47's. Slight surge at cruise so hopefully 46's will work perfectly.
Hopefully, this follow-up will help others... I have seen so many posts that never get fully resolved and always wonder what happened!