TV cable to early Quadrajet

[Cliff Ruggles]

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........

[old cars]

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
        .
        .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.

         

[Cliff Ruggles]

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......

[Kenth]

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:

[Cliff Ruggles]

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.......

[old cars]

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.

[Cliff Ruggles]

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

[tayto]

old cars, are you referring to adjusting this rod to contact the secondaries sooner?

[Cliff Ruggles]

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.........

[tayto]

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....

[old cars]

Install pin as in picture. You will have to be accurate though

[Kenth]

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.

[tayto]

Ok thank you! I will get carb back from friend and recheck

[Cliff Ruggles]

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......

[old cars]

I should Apologize for a previous post with 1970 GTO carb. Those numbers were after I made adjustments. Sorry for the confusion.