Thermoquad tuning on 318

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I have an older Mopar friend that worked in the city Police Garage in the 70's, 80's, and 90's. There were some things that I just have to disagree with him on. He told me that TQ's were designed to have that bog in them.:rofl:
 
Remy.
Sec bog. I mentioned it earlier, about 'tired' AV dashpots, but I will mention it again.
If the dashpot is not new, & it's history/lifespan unknown, then simply disconnect the link arm going from the d/pot to the AV. Wind up the AV spring to 3 turns & test drive. If bog is gone, d/pot is defective.
Another thing when the dashpot is hooked up. The adjustment. I do not know what the manual says, but this WORKS. Gently push the d/pot actuator arm in with the tip of a flat blade s/driver. While held in place, push gently on the rear section of the AV. There should be 0.050" - 0.125" movement of the AV; this measurement is between AV & lug/stop on the airhorn . If more than 0.125", bend link arm to reduce the gap. If there is no movement, bend link slightly [ lengthen it ]. Make sure the link/AV move freely.

Report back with results.
 
remytherat said:
Took the carb off. Took off the top and it turns out the floats were significantly too low. Fixed that. Then I set the idle screw to where there was about 0.020" of transfer slot. Tightened down the pipe plug over the vacuum port which may have been causing a vacuum leak.

Very slight stumble when cold, but nothing like what I was experiencing before. Once it warmed up it was almost completely smooth. I think I will shorten the accelerator pump linkage a small amount to dial it in and possibly go another 1/4 turn on the idle speed screw. It should be good to go in that aspect.

The secondaries have about a 1/2 second bog when I stomp on it but catch right up if I keep my foot pinned. Easing into them at 60mph feels great and 90 comes up real quick. I've never driven a spread bore carb car and the sound...wow. I swear the hood buckles a little. I might try shortening the dashpot linkage a little––I am already 2.5 turns wound up on the spring. What about a vacuum restrictor? Heard old uncle tony talking about that, although I know better than to do what he says without asking other people first. He seems to get away with stuff most of us don't lol

Thanks for the help everyone
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I would run a choke. I like the one from a 73 up truck since there is no electric heater. I'd be tightening up the secondary air valve 1/8 turn till the bog is gone. Pictures of the carb and choke side?
 
The secondaries bog is not always due to the AV spring adjustment......which is why adjusting it does not cure the bog. Logic should tell you that if the factory AV tension is not enough on a stock engine...& this is a stock engine.....then something else is wrong.
Causes of the bog can be:
- AV fully open position incorrect
- & for the 3rd time in this thread: faulty dashpot. The d/pot rubber diaphragms go hard over time & make the d/pot slow to release. Very hard to pick by looking at the d/pot. That is why the test in post #28 will determine if it is a d/pot problem.
A slow to release d/pot creates a rich bog. The AV hangs in the closed position, acting like a choke.
 
Bewy said:
The secondaries bog is not always due to the AV spring adjustment......which is why adjusting it does not cure the bog. Logic should tell you that if the factory AV tension is not enough on a stock engine...& this is a stock engine.....then something else is wrong.
Causes of the bog can be:
- AV fully open position incorrect
- & for the 3rd time in this thread: faulty dashpot. The d/pot rubber diaphragms go hard over time & make the d/pot slow to release. Very hard to pick by looking at the d/pot. That is why the test in post #28 will determine if it is a d/pot problem.
A slow to release d/pot creates a rich bog. The AV hangs in the closed position, acting like a choke.
Click to expand...

Lets cut to the chase here. Stock 318 with 72 340 TQ intake and supposedly stock 72 340 automatic TQ. The carb and intake should work perfectly in this application. Stock 6139s air valve adjustment is 1 turn. This assumes an original, complete, unmolested 6139s carb and choke. Not a fan of throwing parts at something. That is why I ask for pictures. You might be right. You might be wrong. He could have a Frankenstein carb with a 6139s base plate and a newer top plate, who knows what bowl, and missing or mismatched linkage.
 
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I never try to box myself in with any specific number of turns on the air door screw. What if the retaining pin is in a different position on every carburetor? What if the spring is stretched a little? Too many variables there. Just adjust it where it transitions smoothly into the secondaries and be done with it.
 
66fs,
Yes should 'work perfectly'. This carb or any other carb for that matter is only going to work perfectly if all the read adjustments are correctly done. I listed a few things that I know can cause the OPs current problem.
Nowhere did I say to throw parts at the problem. I have a box full of defective AV dashpots that have had the diaphragms stiffen up over time. Time? If original, these dashpots are over 40 yrs old. They cause strange problems. Rubber perishes over time.
 
RRR,
It doesn't matter where the retaining pin is. To adjust, the AV is loosened & allowed to hang. The spring is then wound up until the back of the AV just touches the stop tang. From there, wind up another 1.25 turns. The method of adjustment allows for any manufacturing differences between carbs.
 
Bewy said:
RRR,
It doesn't matter where the retaining pin is. To adjust, the AV is loosened & allowed to hang. The spring is then wound up until the back of the AV just touches the stop tang. From there, wind up another 1.25 turns. The method of adjustment allows for any manufacturing differences between carbs.
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It does matter the condition of the spring.
 
Great Thread .:thumbsup: I know we are talking about fuel metered TQ's. Does all of this info apply to the air metered ones as well? Not trying to de-rail the OP's thread. My carb is an original 1971 model and I am following along and learning.
 
Just revised my last post #33 from info on 6319s TQ to info 6139s TQ. Also should be brass floats set to 1 inch.
 
CFD,
Don't have specific info on the 71 carbs, but the same info generally applies.
The 71 carb is more closely aligned with the Comp Series in it's design.
I do have info on those.
- AV spring: 1/2 turn more after contacting stop.
- AV fully open: 27/32" from choke wall to upper inner edge of AV.
- float level 31/32".
 
Hi all

Got the secondary bog pretty much tuned out. Verified that the diaphragm was in good shape and that the air door opening was in spec. Gradually bent the linkage, and the bog is gone. Tires screech almost immediately.

I am still having a little trouble with the stumble. It almost completely went away with the float adjustment a couple weeks back. That was when it was 85 degrees. No longer so. Car is basically undrivable on a 50 degree morning.
I think that it is simply lean all the way around, given than the plugs look pretty horrible (pretty much no color) and that it likes the mixtures screws about 5 turns out. Car has 4095 jets in it right now. I'm going to try 4098s, which I have seen many people say is a solid starting point.

Doubt this is the case, but it a vacuum leak around the intake ports common? and how should I check?
 
remytherat said:
Hi all

Got the secondary bog pretty much tuned out. Verified that the diaphragm was in good shape and that the air door opening was in spec. Gradually bent the linkage, and the bog is gone. Tires screech almost immediately.

I am still having a little trouble with the stumble. It almost completely went away with the float adjustment a couple weeks back. That was when it was 85 degrees. No longer so. Car is basically undrivable on a 50 degree morning.
I think that it is simply lean all the way around, given than the plugs look pretty horrible (pretty much no color) and that it likes the mixtures screws about 5 turns out. Car has 4095 jets in it right now. I'm going to try 4098s, which I have seen many people say is a solid starting point.

Doubt this is the case, but it a vacuum leak around the intake ports common? and how should I check?
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on the cold mornings, does it eventually work itself out once the engine is up to temp or does the problem persist until ambient temp comes up?

vacuum leak is a possibility. you can use WD 40, carb clean or even brake clean to hunt down any problems at the joints.
 
It starts out really, really bad, getting slightly better as the engine warms up. Its hard to say about the ambient temp, but that does seem to be a factor.

Most people I know here in LA don't run chokes and say they don't have problems, so I think I'm just running much too lean anyhow.
 
remytherat said:
It starts out really, really bad, getting slightly better as the engine warms up. Its hard to say about the ambient temp, but that does seem to be a factor.

Most people I know here in LA don't run chokes and say they don't have problems, so I think I'm just running much too lean anyhow.
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Usually when one has great difficulty getting warmed up it's because it needs plugs, has the wrong plugs, needs more initial timing, or is running too lean.
 
remytherat said:
It starts out really, really bad, getting slightly better as the engine warms up. Its hard to say about the ambient temp, but that does seem to be a factor.

Most people I know here in LA don't run chokes and say they don't have problems, so I think I'm just running much too lean anyhow.
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i think the choke may be a factor. it's likely not the only factor, but it is part of the whole picture.

everybody i know here in LA that daily's anything runs a choke. it's only the fun summer time burger cruiser guys that generally don't, but for all my clients i tell 'em to run a choke.

there's also the fact that two weeks ago it was 100+ and dry and now it's much cooler and damp. so again, not the only issue, but a consideration.

i think you're headed in the right direction. see if you can dial in your advance/curve better. how do the plugs look?
 
junkyardhero said:
i think the choke may be a factor. it's likely not the only factor, but it is part of the whole picture.

everybody i know here in LA that daily's anything runs a choke. it's only the fun summer time burger cruiser guys that generally don't, but for all my clients i tell 'em to run a choke.

there's also the fact that two weeks ago it was 100+ and dry and now it's much cooler and damp. so again, not the only issue, but a consideration.

i think you're headed in the right direction. see if you can dial in your advance/curve better. how do the plugs look?
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Man, I can go out in 20 degree weather, bust Vixen off and she's idling in under a minute, choke adjusted WIDE open and not wired up. Same with Gladys, my truck. The choke operation is for when the engine is cold. If you live in a colder climate, then yeah, it might help out some but if you were brought up driving carburetors, it's second nature with no choke. At least for me.
 
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TQs run lean, that is why they get great mpg. If you have a factory 72 intake, just use a factory choke. You can tune them to run like a fuel injected car if you take a little time. Or you can richen it up and get the same mpg everybody else gets.
 
Remy,
Going to the 098 pri jet is a good idea & will more than likely solve the problem.
Before doing that, you could try this: the small screw in the middle of the met rod hangar. Screw it IN 2 turns. If this helps/works, it indicates leanness. I would then go the bigger jets & return the hangar screw to the original setting.
Today's fuel is a different formulation compared to when these carbs were made. So jetting requirements are likely to change.
 
Update:
A little after thanksgiving i changed to the 098 pri jet, after which I drove the car 35 miles per day until today. Vastly improved everything. Fires right up in the morning with no trouble, even though temps have been in the mid-high 40s. Slight stumble when cold but I have gotten pretty used to it, just have to blip the gas a little harder to get the accel pump going.

I'm thinking of stepping up one more jet size because it likes the metering rods up 3 turns and because the plugs still lack some color. Maybe that's a waste of time since it's really alright.

Thanks all for the help guys
 
Another thing I should add:

I'm looking into getting an advance limiter plate for the dizzy so I can run closer to 16˚ initial without pinging. I also played around with manifold vs ported VA and found that while manifold had slightly better idle quality, ported had vastly improved throttle response. I think this is because the T slot exposure was closer to ideal at idle with ported vacuum.
 
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