General Category > Quadrajet Carb Talk and Tips

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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....

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