Tuner's Secondary Lever Mods

[Papastoy72]

Could anyone with the pics of Tuner's secondary lever mods post them here or if you have done the mods on your carb post a picture of your secondary lever? I would like to try it on one of my carbs. Having trouble visualizing the location of the pickup roll pin. Thanks.

[rgalajda]

Secondary throttle lever and linkage. "Tuner "

The object of this modification is to make a three-point pick-up of the secondary throttle, and to open the secondary earlier in the primary travel and proportion the motion range of the secondary over a larger percentage of the primary throttle lever motion. 

Some early QJets have a secondary lever and linkage that does this. This is just a way to make it with existing parts which are already on the carb you have. 

When the large QJet secondary throttle is opened a large percentage of the primary air flow is diverted to the secondary, resulting in a large change in primary metering signal. If the change is large enough and the A/F metering is close to the edge of the functional range the result can be a sag or stumble, the infamous “Quadra-bog”. 

Modifying the lever and linkage like this makes it so the primary is not as far open when the secondary begins to open. This reduces the severity of influence the flow change has on primary metering. Because the A/F is not disrupted or changed as much the overall carb operation throughout the throttle range is much smoother. 

This linkage deal with the modifications to the tubes shown in the post above this one are the keys to the QJet acting like a very large single barrel with no sensation of primary-secondary, just as smooth increase of power as the throttle is opened.

Before disassembling the linkage, scribe a line over the top of the large outer spring from above the shaft to where it latches under the hook on the throttle lever. Use a small round file to make an elongated slot following the scribed line. A 5/32” chain saw chain sharpening file is ideal for this. 

The roll pin or split pin used for the intermediate pickup point is the one that comes in most QJet carb kits for the accelerator pump lever pivot. The hole drilled in the lever for the pin needs to be very close to the rear edge and near the location in the picture, near the mid-point between the upper pickup point and the slot. 

To achieve correct operation it is necessary to adjust as required by bending the secondary link and the actuation tangs on the primary throttle lever. 

Like a many people surely have, when Doug Roe's QJet book came out in the early 70's I started with the secondary modifications in it and just kept tinkering. I've been doing close variations of this scheme detailed above for nearly 25 years and it works very well on every engine so far, from a 4 cylinder Iron Duke, 250 cu.in. 6 cylinder Chevys, 502 BBC crate motors, Goodwrench crate motors of all variations, Olds, Pontiac, SB Fords from 302 to 427, etc. etc. ...... 

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.

[rgalajda]

Pictures

[Papastoy72]

Thank you Thank you Thank you!!!

[rgalajda]

Those pictures were not my carb.
Here is a carb that I did , a little less drastic with the slot length, and the pin location more centred ( higher )

[rgalajda]

I usually start by bending the arm in the picture towards the other arm. This gives an earlier contact to the secondary. You may be surprised how much difference this alone can make to earlier opening of the secondary. As long as when the throttle is closed the arm still allows secondarys to be held closed , then you haven't gone to far.

[rgalajda]

This is how I measure the initial contact of the secondary opening. Then you you can compare after adjustment and/or modification.
I also take measurements with .400" and .500" primary opening to see secondary opening dimension.

[rgalajda]

The secondary throttle plates should not over centre at WOT. Actually they should be a little less than 90 degrees to full open , or you could upset flow pattern.
You can bend the pin on the throttle shaft to meet the stop, as in this picture.

[rgalajda]

This is how I use the pliers. Do small increments at a time.

[GTO Geoff]

Chrysler tuning tips for WOT position of the TQ sec throttle blades. Blades hanging out below base plate should point IN, towards carb centre. For single plane intake, should be 88* angle; for dual plane, 81*. I suspect this has more to do with air flow distribution, not fuel flow. Probably worth trying on a QJ.