Cliff's Quadrajet Parts and Rebuild Kits
General Category => Quadrajet Carb Talk and Tips => Topic started by: JLBIII on April 14, 2022, 07:18:07 AM
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I have a fresh build 400 engine going in my 68 Firebird. The engine has been broken in and set up by the builder. It also has a rebuilt 800cfm Buick Q-jet with Pontiac linkage on it. Going to put in a TH200R4 transmission with the engine. Looking for help/best options to connect the TV cable to this carb. Thanks.
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I believe there were some quadrajets in the 80s that had the correct linkage/ratio for tv cable
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bowtie overdrives use to make bolt on kits to correct the bellcrank linkage. I would try them, but if it were mine I would do whay old cars says. find the correct factory throttle shaft/bellcrank.2004R or 700R4 use the same geometry.
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The truck carburetor shaft has the correct geometry. I have several that
I have ran with my 700r4.
The CCC car carburetors have an oddball fat acc pump rod which would require
drilling out your acc pump lever or transferring the bell crank parts around.
They are the correct geometry though.
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"It also has a rebuilt 800cfm Buick Q-jet with Pontiac linkage on it."
What is the carburetor part number?
If it is a 1971-74 Buick 850cfm carb (folks call them 800's all the time) the later throttle shafts mentioned will not work as they are too long.
If you are using an early Buick carb and early Pontiac throttle shaft (pre-1972) they are bolt on linkage. Those will be the easiest to work with to add at attachment point for the TV cable.
All that is needed is to fabricate a hook up point the correct distance below center of the shaft to control the 200-4R TV cable.
It's not fussy and only needs to be the correct distance below center and range of motion (distance from) the TV cable bracket.
Adding a hook-up point for the 200-4R and 700R4/4L60 transmissions is relatively easy and many throttle shafts already have adequate material below center to accommodate the TV cable and return spring........Cliff
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Hi Cliff
The carb part number is 7041540. It has a Pontiac primary throttle shaft with bolt-on linkage installed.
Do you know what the correct distance for a pickup point should be?
I have the bolt on linkage from the original carb 7028264 that I could use but would prefer to modify a replacement piece. Still looking for one. Thanks
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here you go
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"If it is a 1971-74 Buick 850cfm carb (folks call them 800's all the time) "
Can you explain what makes these 850 cfm
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Good question.
The 71-74 Buick 455 carbs and the 73-74 Pontiac Super Duty 455 carbs have the same EXACT size as the Edelbrock 1910 and the secondary airflap stop is ground down in the same fashion to provide full opening of the air flaps.
They flow 849cfm
The 1971 Pontiac 455 HO carbs flow 827cfm.
The smaller castings all flow 750cfm, unless they have a longer stop on the air flap shaft. An example of this is the 1968 Pontiac Firebird carbs. They reduced cfm slightly in two ways on those, the linkage that opens the secondary throttle plates has a "step" in it to reduce the open angle and the secondary airflap shaft has a long stop on it to kill off some more cfm.
Tech tips of the week.......Cliff
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Thanks Cliff and everyone who replied!
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The question is : Were these these these flow ratings determined with wet or dry flow. Since there are very few facilities that can provide wet flows but many can provide dry flow testing I can presume these to be dry flow. We know these are not Rochester wet flow testing numbers. Also flow testing can be done one barrel at a time which will skew results. Dry flow testing is approximately 8% higher than wet flow.
850 cfm less 8% = 782CFM ratings
Read This
Sometime during the 1950’s, engineers found that a passenger engine with a four-barrel carburetor would not maintain a vacuum of 3 inches of mercury at wide-open throttle; and by some convention 1 ½ inches of mercury was chosen for rating 4-barrel carburetors. The ratings for 1-barrel and 2-barrel carburetors were left unchanged.
To convert from one system to another (with a very small percentage of error) is relatively simple. Simply use the square root of 2 (1.414). Thus to convert a two-barrel rating into a four-barrel rating, divide the two-barrel rating by 1.414. To convert the four-barrel rating to a two-barrel rating, multiply the four-barrel rating by 1.414.
This worked very well up through the mid-1960’s, when carburetor comparison tests became popular in car magazines. One carburetor company determined that the results could be skewed by rating their carburetors “dry” (air only), instead of the conventional “wet” (a non-flamable liquid with the density property of gasoline and air mixed). Rating the carburetor dry would add approximately 8 percent to the rating (example – a carburetor rated on the four-barrel rating scale at 500 CFM would now amazingly flow 540 CFM).
As the general public was unaware of the “wet” versus “dry”, this system worked fairly well until the mid-1980’s when it seems that other scales were “needed”. No attempt will be made to explain ratings of carburetors produced after 1980. The best way to compare these units would be throttle area (which was a measurement used back in the 1950’s and 1960’s); or more accurately, the comparitive area of the main venturi. On the later carburetors, best to write to the company, and ask at what vacuum the carburetor was tested, and whether it was tested wet or dry. If this information cannot be obtained, then the rating is suspect.
So, to give an example of the 4 ratings scales prior to the mid-1980’s:
Using a Carter 4-barrel AFB carburetor that is rated wet and rated 500 CFM for an example.
To convert this rating to the 4-barrel dry scale, add 8 percent (multiply by 1.08). 500 CFM multiplied by 1.08 is 540 CFM.
To convert this rating to the 2-barrel wet scale, multiply the rating by the square root of 2. 500 CFM multiplied by 1.414 is 707 CFM.
To convert this rating to the 2-barrel dry scale, first convert to the 2-barrel wet rating as above, then add 8 percent. 707 CFM multiplied by 1.08 is 764 CFM.
Going the other direction, if we take a Rochester 2-GV carburetor that is rated wet and rated 435 CFM.
To convert this rating to the 2-barrel dry scale, add 8 percent. 435 CFM multiplied by 1.08 is 470 CFM.
To convert the rating to the 4-barrel wet scale, divide the rating by the square root of 2. 435 CFM divided by 1.414 is 308 CFM
To convert the rating to the 4-barrel dry scale, first convert to the 4-barrel wet rating as above, then add 8 percent. 308 CFM multiplied by 1.08 is 333 CFM.
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I'm not sure what method Edelbrock used to test their 1910 "850" cfm units. The 1910 is nothing more than a 1904, 1905 or 1906 with a shorter stop on the secondary shaft allowing them to open a tad further at WOT. The added holes and bent up "notched" flaps do NOTHING at all to improve cfm over the standard units. All of those units are based on a 1980-81 Chevy truck Q-jet.
I had a good friend with a flow bench make comparisons using one half of the carb to verify the numbers. He also used mathematical calculations to compare the results to carburetors (Holley) that were also tested.
He came up with "849" cfm for the later q-jets (larger castings) when the air door stop was ground as shown in my book.
The smaller castings were right at "750" cfm, the 1971 Pontiac 455 HO carb "827". He even tested a later carb with the outer booster rings removed at "897" cfm.
Matters not in the big scheme of things. What does matter is the power levels they will support.
Right on the dyno I've back to back tested a Pontiac 750cfm Ram Air carb, a 1971 455 HO carb, and my 1977 Pontiac carb set-up same as an Edelbrock 1910.
The engine was a 455 making right at 514hp. All carbs tested were equal to 4500rpm's then the two larger units showed a little more HP to peak power. There was almost no difference between the HO carb and my 1977 Q-jet.
I finished the testing at a private track rental. Remarkably the smaller carb wasn't much off the larger ones for ET or MPH, and the 455 HO carb ran the highest MPH for all runs even though it flows slightly less than the 1977 unit.
The entire spread of ET for all test runs was less than .05 seconds and just less than 2 MPH. The problem with track testing for cfm is that the car leaves just as hard with each carburetor and spends very little time up neat the shift point for the entire run. Folks who drag race will understand this and see why CFM isn't as big a player with these things as most would think.
I would also mention that I supply carburetors for vehicles use in FAST and Pure Stock racing. We've got a few into the high 9's on 8" wide bias ply tires. This clearly shows that a well set-up Q-jet is very capable as a "high performance" carburetor as the vast majority of folks reading this have cars that are much, much slower.........FWIW........
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Since they were based off the truck carb, did they have truck secondary linkage or car?
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Edelbrock pretty much duplicated the 17080212/213 truck units when they designed the 850 cfm 1910. They gave it a "fat" idle calibration and did some dumb work to the secondary air flaps. They also used a front pull-off with link up to the secondaries instead of a rear P/O with two links on it.
Nothing really "special" about a 1910 and if you know what you are doing you cam build one yourself from any 1979 or later truck carburetor.......
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"Since they were based off the truck carb, did they have truck secondary linkage or car?"
17080213 is a truck secondary linkage . I don't have a 1910 Edelbrock here
All of these truck linkage carbs have a late opening secondary and can benefit from manipulating this linkage to quicker opening secondary. The early quadrajets with the 3 point opening secondary linkage are the best, but all can be manipulated. Getting the secondary to open sooner is what works good because of the very small primaries. It will not effect cruise conditions if done right. This is where square bore carbs have the advantage. I adjust all quadrajets to have an earlier opening secondary, except for very few applications . It makes for smoother feeling driving experience and more responsive at lower speeds.
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The main benefit from an early open point would be drag racing a "foot brake" car. The micro second saved when you stomp your foot to the floor to launch the car might show up on your times slip as a little quicker R/T or 60', but it wouldn't be much.
Actually you will enjoy a greater driving experience with most applications by having more of the primaries available without having to get into the secondaries, plus use less fuel for many driving scenarios.
The factory used the higher pivot point on a lot of baseplates not just those found on trucks. Having more of the primary cfm available without getting into the secondaries allows for higher cruising speeds on the primary side of the carb. You can also climb steeper grades in higher gears without having to use the secondaries or downshift to a lower gear, which is advantageous for larger/more powerful engines pushing heavier vehicles, towing, etc.
Not exactly sure what is meant by "manipulating" the linkage. The only adjustments required on any Q-jet baseplate are to make sure that it doesn't hold any of the throttle plates open at idle speed or when they are supposed to be closed, and to make sure the huge secondaries can reach their full open point at WOT........FWIW........
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Here is a few examples.
I use vernier caliper from the underside of the throttle plates, flat against the butterfly
1970 GTO 7040264 (original 3 point opening secondary linkage)
.300” primary ---- contacts secondary
.400” primary ----.060” secondary opening
.500” primary ----.410” secondary
1968 Chev 7028313 ( original later linkage system/ chevys had already changed )
.360” primary contacts secondary
.400” primary no opening on secondary
.500” primary ---- .250 secondary
1978 Chev Truck 17058213 ( later truck style linkage )
.470” primary ---- contacts secondary
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.500” primary no opening on secondary
1978 Chev Truck 17058213 – After changes to linkage
.300” primary ---- contacts secondary
.400” primary ---- .070” secondary opening
.500” primary ---- .370” secondary opening
This truck carb I had installed on my 454/500 hp Monte Carlo . Before I made changes to the linkage it was very flat at lower speeds. Too much throttle movement required. After changes it was closer to the ( x ) carb I was used to. I did not see any downside to the changes.
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Even after all that I don't fully understand the posts.
Are you saying that your engine feels "flat" on the primary side and required the secondaries to make decent power.
It appears that you are adjusting or manipulating the cut-in point and suggesting the earlier the better?........
In any case I'll say this. The 455 in my Ventura is 11.3 to 1 compression, well chose cam, and good flowing heads. It has instant throttle response right off idle, and STRONG power at lower RPM and lower vehicle speeds without getting into the secondaries........and it NEVER feels "flat", sluggish, down on power, etc for any "normal" driving scenarios......
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Since they were based off the truck carb, did they have truck secondary linkage or car?
Jim, in Cliff´s book page 120 there is a picture of the Edelbrock 1910 secondary linkage (pass. car).
I added pictures of my 1904 and 1910 here:
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Coincidentally I have one of each in the shop at the moment. The 1904 has a defective casting so it's junk. That's the 3rd or 4th defective Edelbrock Q-jet I've seen to date, so it's not that common but something that needs to be checked when you are working on one.
I fully understand the different secondary linkage and how one allows more throttle angle that the other before it reaches the cut-in point. I've ran/tested many hundreds of samples of both on my engine and never really noticed any difference in performance delaying the cut-in point a little further.
Most likely the factory used the truck or delayed open point to simply allow one to load the engine more for heavy work, towing, etc so you could climb steep grades and such without having to get into the secondaries as soon.......
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No matter the motor, they all need their individual appetite satisfied as far as idle circuit, main jet, rod and spring, secondary rod and hanger, etc. but this secondary set up is universal. In other words, the same basic secondary mods but tune the carb to each engine.
The single common denominator in the feedback from users is how smooth and progressive the throttle feel is with this setup when opening or pedaling the throttle. This makes a QJet into a superior circle track and road racing carb. The secondary linkage modification is a very important part of this.
A QJet for a jet pleasure boat for example, I would delay the secondary opening as much as possible. If it were an actual race boat, in that case open as early as practical. Circumstances alter cases.
Because of the variations of QJet secondary linkage and levers, no two I do are exactly alike, though they are similar. If it is a hotrod, opening the secondary early will be appreciated by the driver because it apportions the secondary air flow, and so engine power, over a wider range of throttle travel. Opening the secondary earlier make it so the opening rate is more gradual and that gives the driver more of a sense of linearity in controlling engine power. It eliminates the sensation that 80% of the power comes in the last 20% of pedal travel. Early opening spreads the power out over more throttle pedal travel so 50% feels like 50%, etc. Drivers like it. For example, it isn’t the right thing to do for a truck intended for towing, but a sporty truck with no trailer hitch, all lowered with shiny paint and custom wheels, the driver will like it.
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It used to be very popular to run one to one mechanical linkage for drag racing.
It makes those carburetors a PITA to drive back the return road and thru the pits efficiently, but Racers with carbs set up in that fashion claimed they were quicker and more consistent in R/T's and short times, etc.
Now that it's more common to run electronics and leave with the accelerator on the floorboard (WOT) we don't see nearly as many full race carbs set up in that fashion.
I "adjust" the secondaries on every Q-jet I've ever built here. It's actually quite rare to find one that doesn't need considerable "tweaking" with the linkage to make sure the primary throttle plates can fully close and secondary throttle plates reach their full open point.
About 90 to 95 percent of the carbs I take in are NOT set-up correctly. I'm assuming it wasn't part of the assembly process at the factory to insure the linkage was correctly adjusted, at least from what I've seen.
As far as the Edelbrock 1910, really nothing "special" about it anyplace. It was set-up to be pretty rich for idle fuel, but there were many versions of it made. The one I just worked on in the shop had tiny idle bypass air holes, some were much larger. Different size idle tubes were also used in them. DCR's, upper and lower IAB's, and jets/metering rods were pretty consistent otherwise.
Haven't seen a single example yet where the secondaries reached 90 degrees, most roll past center, where others didn't reach the full open point.
I've probably worked on at least 200-300 of them since going full time back in 2003. They have fundamental flaws in them requiring modification to make them an effective "race" carburetor, especially drag racing on cars that leave really hard.
I'd also add here that the Q-jet makes an excellent Marine unit, even for high performance Marine use. It does equally as well for off road applications that see steep angles and a lot of bouncing around. I've set up quite a few for truck pulling as well as they tend to start wheel-hopping at the end of the pulls. The small centrally located fuel bowl, excellent hinge pin/float arrangement (later units) plus jets on the bottom of the bowl are advantageous for that sort of work. They do very well bouncing around in rough seas or rough terrain. I get calls for them all the time for those applications........Cliff
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old cars, are you referring to adjusting this rod to contact the secondaries sooner?
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The "when" it contacts to start reward movement is on the other end of the linkage.
There are several different types depending on year, model, etc, but they all basically do the same thing. As the primaries reach a certain point parts intersect to start moving the link reward to open them.
It is RARE to find one correctly adjusted and a place where a LOT of novice builders don't catch factory mistakes (or some "cobbling" before you got there) so the build is doomed before it ever gets started.
Those parts circled often need some minor adjustments. There MUST have some clearance between them when the primary plates are closed so the secondaries can fully close or you are in trouble.........
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Cliff, probably should start my own thread but will ask anyway. I did a marine Qjet a while back (with your kit), and adjusted the rod in the picture to set the secondary blades 90* when full open. There was no pin I could modify like on a late Qjet to make a poative stop. Was this not the correct way to go? Carb has yet to go into service, maybe this summer....
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Install pin as in picture. You will have to be accurate though
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No need for an added stop on sec shaft if pri to sec is properly adjusted.
1. When rod meets lever, (yellow),
2. rod is in center of hole in lever, (orange). To adjust, bend rod, not lever.
3. Then adjust closing of secondaries, (green).
4. And last adjust for proper sec blade opening angle, (blue).
Also, not only M4M Truck Qjets uses the tall lever on pri shaft for the sec rod, f.e. late 70´s Olds Car M4M Qjets uses these too.
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Ok thank you! I will get carb back from friend and recheck
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Marine Q-jets use different linkage than shown in the pic. Simply set them up to fully open and if you want to insure they always stop at the same point you can gently bend the front tab so it contacts the bottom of the link at the exact same moment....they aren't fussy and it will come to the same full open point each time you go to WOT......
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I should Apologize for a previous post with 1970 GTO carb. Those numbers were after I made adjustments. Sorry for the confusion.
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We've taken a very simple topic and made it a LOT more complicated than it needs to be.
For 99 percent of the hobbyists who have decided to build, tune, and calibrate their Q-jet, baseplate rebuilding is an important part of the process, no doubt about it.
What MUST happen is that the person doing the work takes steps to insure that the HUGE secondary throttle plates are correctly adjusted to fully close and not allow air past them or a vacuum leak at idle.
They follow suit by adjusting the primary plates for full closing and making sure that bushings are installed if/as needed, plus tweaking the shaft if it is bent or twisted.
The linkage on the primary shaft can be incorrectly set-up on a stock carb as they were mass produced items. Matter of fact it's pretty rare to see one that will fully close and when move to WOT has the secondary throttle plate fully open as well, let alone all the throttle plates fully open simultaneously.
This is where the builder needs to pay close attention to detail starting with indexing, centering all the throttle plates for full closing. Then move on to adjusting the linkage so they fully open. Some models have provisions for a stop so the secondaries don't roll over past center, others do not.
You will also find more times than not the primary throttle plates are either over or under center when the seondaries reach the full open point, hence the need for adjustments in a few areas to make sure all these things are happening as they should.
Good results come from close attention to detail. I use and recommend a positive stop IF it is available, and nothing wrong with modifying things or making one when it's not.
As far as adjusting the open point or angle of the primary throttle shaft when it starts to open the secondaries, it's just not a main priority vs having everything else set-up as it needs to be. As the driver of your vehicle you should at this point in your learning curve know how to mash your right foot down hard and fast enough to get the secondaries on line if/when they need to be.
When I build or restore a Q-jet here, or any other type of carb I spend a LOT of time with the baseplate. Often machining it flat on both sides, installing bronze bushings, indexing/centering all throttle plates for full closing with the absolute MINIMUM amount of light showing, etc.
Time spend in each area of the build, being meticulous and close attention to detail is what sets your build apart from the rest and another important part of making sure that you get a good end result........Cliff