I posted a question about my poorly functioning 66 Toronado a few weeks ago and due partially to several suggestions from this site decided it was the 4 barrel that was the culprit (actually for a 350 Chevy truck) on my car.

(I will duck after saying this next part)

I decided due to costs to go ahead and rebuild the old carb and remount it. I did and the thing works very well, with one exception. The secondaries don't seem to be kicking in. I converted the carb to a manual choke (because I always liked them and the 350 Chevy carb wasn't linking up well to the choke spring anyway). So to convert to a manual I had to remove some of the choke linkages that weren't functional anymore anyhow.

So my question is what causes the secondaries to open? If its simply manifold vacumn then there is nothing I did that would have interfered. Or is there some sort of linkage that I might have removed?

One more thing, I used my hand to throttle the engine fairly hard and looked over into the carb, the secondaries never budged.

Thanks for any help/ideas.

"Checkov"

 

Vacuum. The tension spring on your upper valves might be too tight. Just had a similar problem with mine.

 

Sorry, one more thought. I can never get mine to open sitting in park.. Not sure that is a good idea anyway. Engine has to be under load.

 

Thanks, Jeff. Did you adjust yours ( and if so, how?)

 

Don't confuse the secondary throttle plates with the secondary air doors. The throttle plates are opened by a mechanical progressive linkage. The secondary air doors (looks like a choke plate on the top of the rear 2 barrels) is vacuum operated. You should be able to look down in the carb with the car shut off and observe the secondary throttle plates move by advancing the throttle linkage. You will need to hold the secondary doors open with a screwdriver to look down in the carb to see the throttle plates move. The secondary doors do not open by reving the car in neutral. The engine needs to be under load for them to work.

 

Thanks Sampson, it makes more sense now.

 

There is often a link at the fwd edge of the upper secondary valves, RH side, that prevents the valves from opening until and unless the choke is 100% open.

Don't look down the carb of a running or cranking engine, use a mirror if need be. First start of a new engine last week, I was reminded of this when flames shot up to the hood upon backfire. Then you gotta put the fire out too.

Watch the outer end of the 2' [secondary] throttle shaft to see if it is turning [engine off]. And/or prop choke all the way open, manually open 2' upper air valves, and verify that the lower 2' are opening [all the way].

It is common for an engine in park to require some good bit of time for the upper 2' valves to open. Also, they are caused to open slowly by a link to the choke vacuum break diaphragm on the RH side. The car's RH side, not yours. In practice, this is a great system. You can remove the vacuum line from the choke pulloff for operational checks. [let it happen faster] Of course if the engine is off, there is no vacuum at that diaphragm anyhow.

 

It's technically air flow, not vacuum (the vacuum signal is highest when the throttle blades are closed). When the lower throttle blades open, the air flow into the engine increases, and the air valves open in response.

 

Excuse my ignorance on QJets but aren't the secondarys top butterflys regulated by a spring that lets them fly when the engine needs it? Maybe this spring is corroded or out of tune?

 

Since you removed a bunch of the choke linkages, the secondary lockout might be held closed by gravity. There are two basis styles: secondary throttle plate lockout and secondary air valve lockout.


Here's the throttle plate lockout style:




Here's the secondary air valve lockout. You can see the tang above the forward edge of the secondary air valve:


This is the tang:

 

Fun71, the first look more familiar.

 

yes there is a spring to adjust tension on the secondary upper flaps.if you look in this first pic where the link hooks into the end of the upper flap rod,right behind it is a flat head screw.this adjusts the tension of the flaps BUT it is held by a set screw that comes up from the bottom.it has an allen head.so to adjust hold the screw and loosen the allen bolt then turn clockwise to tighten,counter to loosen.as you do this push down on the flaps,i used to run the spring so when you push em down they just flop back shut,but its also a trial and error kinda thing.adjust how you like em.

 

Cherokee, thanks. To loosen this screw you have to loosen an Allen bolt. Can that be reached from the outside of the carb or does the carb have to be removed and disassembled ?

 

^^^THIS!!!

The Qjet is NOT a "vacuum secondary" carb. It is a mechanical secondary carb, with air valves that are opened by mass air flow, NOT vacuum. (FYI, on a true vac secondary carb, the vacuum signal is venturi vacuum, not manifold vacuum. Venturi vacuum is low with the throttle blades closed and high at WOT)

The difference between this an a vacuum secondary carb (which will always have a large vacuum actuator connected to the linkage) is that on a vac secondary carb (like a Holley), if you were to block the secondary openings on the carb, vacuum in the primary side would still open the secondary throttle blades. On a Qjet, if you tried this, the secondary air valves would not open, since there was no airflow in the secondary venturies.

The Qjet secondary airvalves are essentially a mechanical mass airflow system, like on modern EFI systems. Mass airflow through the secondaries not only controls the airflow through the secondary air valves, it also controls fuel flow through the position of the secondary metering rods. Once again, the Qjet is arguably the most advanced 4bbl carb ever made.

 

yes to loosen the screw the allen bolt needs to be loosened first,and no you do not need to take the top off.most allen wrenches have a long and short side.stick the short side up into the bolt and loosen while holding the screw still.and when moving the screw right or left it doesn't take much move a little then lock the allen bolt and try it if you need more repeat

 

One could argue that air will not flow across the secondary air valves unless there is a pressure differential to cause said airflow. Delta-p: the driving force behind fluid flow.

One could further assert that this pressure differential means that, by definition, there is "some" vacuum under the air valve with respect to the static pressure of the air above said valve.

When the lower secondaries are initially opened, and the uppers have not yet been allowed to by that link to the choke pulloff... the bottom of the secondary air valve is indeed fully exposed to whatever manifold vacuum happens to be at that time.

Thus the delta-p

thus the airflow

thus the opening of said upper air valves, working against the secret hidden spring [I can't believe you guys let that secret out!] and the link from the choke pulloff [I can't believe no one else mentioned this CRUCIAL part...]

If the OP removed that "useless" link to the choke pulloff, the secondaries may never work quite right. One should understand the function of each part, and its interactions, before making modifications. I know, it seems like a lot, but the number of links and parts and functions is actually finite, and folks a lot less clever than you or I have learned this stuff....

How about a photo of the RH side of this now-manual-choke Type C carb?

 

IMO...I doubt this adjustment is where you need to be playing around for the problem your having. Usually the air door needs to be tightened up slightly as the spring weakens over time and generally causes Mid to WOT throttle bog due to premature AVS door opening (secondary rods unseating too soon) dumping in more than the desired amount of fuel(rich) AKA Quadra-bog.
I suspect (as mentioned) you have a problem with the linkage, the lock out, the choke or the pull off. I would go at these items first.
The AVS setting is generally a very fine tuning adjustment not a big **** adjustment. Turning the wrong screw on a Q-Jet only leads you to trouble & frustration. This is how they have a bad wrap with the uninformed as being problematic to play with.
Note this is a sensitive adjustment. You can do it with the carb on the intake. If you decide to adjust it I suggest you pull the horn and really look at it and do it on the bench first then do it on the car. You need to know where you are starting so you can go back to that if needed. Hang on to it as your loosening the spring because it will ...well spring back to the relaxed position. Not good as you will lose where your starting point was. Before you go any further I highly recommend Doug Roe and Cliff Ruggles Q-Jet books(Bibles). Both books have a wealth of easy to understand info. Worst case (or best) is you could send it out to one of several respected Q-Jet rebuild shops for a good thorough once over. Well worth the money to get a Q-Jet back to top performance. Then you can do some small tweaks if needed to "super tune" it to your application(along with the ignition/timing curve).

 

yes correct what works on my engine may make yours run worse so a little at a time is the way to adjust it but enter at your own risk!also if you removed the choke housing you uncovered a vacuum port.if you look at the bottom pic of the choke side the bracket that holds the choke pull off.the very back and bottom of that bracket has a rounded ear.that is covering that vacuum port.

 

post a pic of the carb and a pic of the choke side so we can see.also the 66 toro carb is different then any other q-jet

 

It's cold out there today

 

Oops, that is my spare carb with the choke still attached.

This should be the right one.

 

ok that vac port is covered BUT the vacuum T on the hoses right in front of it is broken.also didn't the toro fuel line stick out the front rather then to the side.olds always went out the front and had the long fuel filter.chevy went out the side with a short filter.also you need the hold down screws not bolts.i like the screws as it's harder to overtighten.how bout a top pic.

 

Remember , this is a quadrajet for a 1974 Chevy 350 that someone installed before me. I didn't have the right carb and choose to rebuild instead of buying a rebuilt from autozone or a new Holley etc ($23 versus $200 versus $400).

( ironically I sold the carb off my 67 Toro parts car before I realized mine was not stock).

 

Your vacuum break and diaphragm and your air valve dashpot are missing.

That'll screw up smooth running.

- Eric

 

I noticed something else. With my spare carb I pull the accelerator linkage forward, as if a person was giving much gas, and the lower accelerator plates are mechanically opened. I can imagine that would create a pull/air flow that would open the top air doors.

However on the carb on my car I looked down into the carb secondaries by holding the air door open and when I pull the accelerator linkage forward it is not giving any movement to the accelerator plates.

My hypothesis is that when someone slapped a quad off of a 350 Chevy onto my toro the accelerator linkage from the toro does not pull enough for the new carb ???? If that is true I wonder if the linkages can be adjusted???

Yeah I see the broken T, wasn't broke last time I looked at it...dang gremlins.

Thanks all.

 

oh by the wording of this statement i thought it had a 350 chevy carb and you decided to rebuild the old(original) carb.
if your looking for one i might have an original carb and the front hold down screws.

 

so if your pulling the throttle back and look down the carb the front ones should open about 3/4th the way before the rears start to move.then they open full in the last 1/4 of the fronts.if you still can't get them to move i would pull the carb and try it off the car.maybe you have a gasket issue.

 

Your missing the progressive linkage rod would be my guess, How about a photo of the other side of the carb?
Did you have any "spare" parts left over after the rebuild? Google some pictures of Q-Jets you will see what Im describing.
The horizontal rod down low on the throttle base plate is the one Im describing.

 

Of carb

 

Sorry, Chris, but that's kinda like saying that a speed-density EFI system is the same as a MAF EFI system. They are not, and the Qjet is not a vacuum secondary carb.

A vac secondary carb uses venturi vacuum in the primary bores to actuate a vacuum diaphragm that opens the secondaries. Just like a speed density EFI, this is "open loop". The diameter of the secondary vac diaphragm and the rate of the spring inside it is what determines the opening rate of the secondary throttle blades.

On a Qjet, as in a MAF EFI system, the actual mass airflow through the secondary air valves is what causes them to open. The reality is that the delta P you are talking about is LESS at WOT, when the valves are open the greatest, so it isn't vacuum that's opening them. In fact, when the air valves are fully open, manifold vacuum (and thus that delta P) is near zero.

 

Okay. You have no idea how this carburetor is supposed to work, and can't tell whether it is working properly.

You need to read the Rochester QuadraJet Manual, preferably with a QuadraJet in your hands as you read it, and then get back to us.
Learn it. Love it. Live it.

Here's what I see in your pictures:



When you step on the gas pedal, the lever above the pedal pivot pulls the throttle cable backward, as indicated by the blue arrow.

This pulls on the top of the throttle plate lever, and causes the throttle plate lever to rotate clockwise (as viewed from the left side), which pushes the secondary throttle plate actuating rod (inside the red oval) toward the back of the car, thus rotating the secondary throttle plate lever (yellow circle at the top end of the lever) clockwise and opening the secondary throttle plates.
The end of the secondary throttle plate lever, as indicated by the yellow circle, follows the trajectory of the yellow arrow, until it hits the edge of the throttle body flange, which serves as a stop.

If this isn't happening, there's something wrong.







Here on the right side of the carburetor, you can see the opposite end of the secondary throttle plate shaft in the yellow oval. The metal rod that passes through the shaft is the choke lock-out. A piece of the missing choke linkage engages with this piece when the choke is applied, preventing the secondaries from opening.

The red circle indicates the place where the secondary air valve dashpot linkage is supposed to connect.
It's not there.

The blue circle indicates the location where the secondary air valve dashpot is supposed to be.
It's not there either.

The secondary air valve dashpot is a slow-bleed vacuum device that prevents the secondary air valve from opening while vacuum is high (and demand for power is low), and also slows the opening of the secondary air valve, thus preventing sudden opening, which would stall or bog the motor.

Go read the book, now, Grasshopper.



- Eric

 

That is a fantastic tutorial. Well done.

 

Thank you. I do try.

Basically, if you're doing anything more than just basic adjustments on an otherwise healthy carburetor, you've got to read the book, or the appropriate section of the CSM.

- Eric

 

Thanks. I can take my hand and twist the secondary throttle plate lever very hard, meanwhile looking down into the carb., and the secondaries barely open. With the spare carb I have when I do this they secondary plates open very well.

So I shall pursue the book you gave me.

Have a good evening.

 

You're lucky you've got two carbs to mess with, so you can get a feel for these things with your hands on.

Since there's clearly something very wrong with the carb on the car (or the way it's mounted), you should really take it off, empty it out, and just sit down with the two of them and go through them piece by piece, while reading the manual. Once you see it all working right, you'll really understand it, and it'll stick with you for the rest of your life.

- Eric

 

Or just get a Holley. chuckle

 

That's an option, as is an Edelbrock, or a replacement QJ, but the OP specifically said he was trying to avoid spending money if he doesn't have to, so using his own brainpower and time (which are free) may get him to where he needs to be without spending more cash than he needs to.

- Eric

 

Except for possibly the Carter Thermoquad....


Yes, the 1966 carb is different, in that it has a dashpot connected to the secondary air valve....but it has been over 40 years since I worked on these......and CRS is setting in!

The best advice I can give is to study everything about these carbs that you can, from either Factory service manuals, or aftermarket tuning manuals, tips, etc. For the most part, they worked fine then, and should work fine today ......(with the exception of what we are buying today that is labeled "gasoline")..........

 

Imitation really is the sincerest form of flattery...

 

No argument there, Joe!! 1966 vs. 1971.......lots of stuff happened in those years....

I am familiar with both the Qjet, and the Tquad, but it's been a long time since I've worked on the Qjet.

I worked for Chrysler for 16 years, starting about when the Tquad was introduced, and am much more familiar with them.....I was an Olds man long before that, so I do know a little about the Qjet, too.....just haven't had any in a long while................too long, in fact!