Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: bob69 on May 19, 2022, 05:27:54 PM
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Cliff, in all of the testing I've been doing with the 7029207, I've noticed that the afr's in the 1000 to 1500 rpm range have been on the rich side. No matter which jet/rod combination I use the afr's in this transition range are in the low 13s. Even when the idle afr's are set to the 14 range the 1000 to 1500 rpm are still in the low 13's.
The 7029207 is known to have generous idle fuel. But what if your combination does not need the extra fuel. Is there a way to reduce the fuel flow in this off idle range.
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Are you noticing negative running symptoms thru transition or just watching a gauge?
There were several different "recipe's" used on the 7029207 carburetors depending on if they were original units or Service Replacement.
When used outside the original application (350/350hp) you may need to install slightly smaller idle tubes and or DCR's to clean things up at idle/off idle. I've had to do this a few times when 7029207 Service carburetors were being used on the 350/300hp or engines with smaller cams in them.......
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Cliff, drivability is OK but I would like to increase gas mileage. I have a 50 mile pleasure drive that I make often. Speed averages between 35 and 45 mph. The car burns around 3 1/2 to 4 gallons of gas - mpg around 13 - 14 mpg.
Gas milage should be a lot better with a mild sbc 350, 200r4, 3.55 rear. Engine rpms are in that 1100 to 1500 range.
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The 7029207 is a service replacement carb. The date code (2602) suggests it was made in 1982.
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Not likely to do anything with the AFR, but do you have working vacuum advance?
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77cruiser, I hooked up a vac pump on the dist vac adv and it holds vac and the points plate moves as expected. All looks ok.
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7029207 idle tubes are in the .038"-.039" range, but i have seen units with .035" as well.
7029202 idle tubes are in the .034"-.035" range.
Only way to reduce idle and off-idle fuel is to replace large idle tubes with smaller.
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bob69, Hopefully the smaller idle tube will fix you up but consider this.
Your original post says you have a stall converter of 1800 rpm, your cam rpm range is 1600 to 5200 rpm and your getting less than optimum MPG in the 1100 to 1500 rpm range at cruise speed.
Maybe better MPG is just not in the cards for those conditions. ...???
I bet it does better at 60 mph down the open road. Does your converter lock up?
I aint know, I,m just axing...
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Kenth, I have four 7029207's. All are SR carbs. Three have .037 idle tubes, one has .038. All have .053 down channel restrictions. Three have .081/.063 upper/lower idles air bleed. One has .079/.062 iab. The larger iab are on 1982 and 1984 carbs. The smaller iab are on a 1976 carb with the .038 tubes.
The 1976 carb is currently on a 400 sbc and it runs great. The 400 gets better gas milage than the 350 when I keep rpms in the 1200-1500 range. The cams are simular, 214/214 110 lsa on the 400 and 214/224 112 lsa on the 350. The 350 should have better gas milage.
I also have an original 7029202 DH E9 carb. Idle tube -.035, dcr - .053, uiab - .068, liab - .065. It was tested on the 350 and the afrs were leaner than the 207s. But is it due to the smaller tubes, smaller iab, or both.
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Quadrajam, good points. The 200r4 goes into lock up at 30 mph under light throttle. So the stall should not be an issue at the rpms I'm looking at.
The rpms are below the cam's operating range so it's not making best power, but at light load conditions it does not need a lot of power. When needed the 200r4 will down shift nicely. I should still be able to lean out the carb so it gets better gas milage. I hope.....
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All the 9202 Qjets i have notes on has the same size upper and lower idle airbleeds as the 9207´s, .079"-.081" uppers and .062"-63" lower bleeds.
Down channels in both are in the .051"-.053" range.
Only difference in idle/lowspeed circuit is the idle tube size,
Larger airbleeds equals leaner mixture, just like smaller idle tubes.
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So I've made some changes but the carb still runs rich at low rpms. The idle tube was changed from .037 to .035. With no other changes, the afr's changed from around 13.2 to around 13.6. Not as much as I was hoping.
Next, the float level was changed from .250 to .375 in the hope that lowering the float level would lean out the carb. I did not see much of a change in the transition rpms. However the afr's did get leaner some in the 1600+ rpms. The most notable change was in heavy accelerations. Performance felt down.
I checked the secondary hanger to see is the secondaries were too high. They were within specs. I did notice the transfer slots were exposed around 60% at idle. Not sure if this is normal for a 7029207.
Any other suggestions?
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Next step i would open idle bypass air from .073" to .095"-.100".
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Kenth, the original IAB was .098. It was opened to .110. The afr's on the initial test were around 14.1 in the 1300-1700 rpm range. Exactly what I was looking for. The idle screw was closed 1/2 to 3/4 turn. The idle needles were adjusted leaner - 1/4 turn. The IAB holes were .110 with a smaller .098 restriction at the end of the hole. Very easy to drill out.
Now I have a new problem to solve.
After driving around a bit, I did a medium hard acceleration. Afterwards the afrs dropped to the previous 12.9 to 13.2 range for cruze and idle. By chance there was road work up ahead causing a 1 mile backup. Never got on the gas as we crepted along. The afrs kepted getting leaner. After about five minutes the afrs were in the mid 14 range. Idle was deteriorating.
After the road work, the afrs stayed in the low 14 range while driving slow. But as soon as I gave it some pedal the afrs went back to the low 13 range. After that the afrs would move around a bit. In the low 13s at times, then changing to the high 13s at times.
Any ideas as to what is causing the afrs to change like this.
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Sounds temperature related. Was it hot weather then? Carb
getting hot??
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Bob, i have notes on at least 10 original and SR 7029270 units, all have idle bypass air in the .072"- .073" range, so i guess your carb has a later years throttle plate if you found .098" IBA.
For the inconsistent AFR i would look at the float system, fuel pressure/volume, inlet valve and float setting.
FWIW
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Quadrajam, I doubt heat was an issue. Air temps in low 70's. Temp gauge was reading about 180 even with the long idle times.
But I did experience a sticking air valve once, on a diff carb, when when it was hot. Functioned smoothly on the bench and when cold. But was binding after the engine was hot. So I checked for that on this carb. Air valve was not sticking.
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Kenth, I checked the throttle plates on the five 7029207 carbs I have. All throttle plates have a stamped number on the passenger side rear. The numbers are 37554C, 37554S, 7554, 37554C and 37554E. Pretty sure they are all original to the respective carbs. The smallest IAB was .098.
I've installed Cliffs N/S, float and filter from his kit. The float is set low at .375. So I'm thinking these are ok. The fuel pump is a new Delphi MF0001. Listed at 5 psi. Have not seen any indications of flooding,
Anything else I can check?
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So I could never get the 7029207s I've been working on to tune/run correctly. The idle and off idle afrs would not stay stable. One was due to a soft casting material and the other had voids in the base plate. Just bad luck to have two defective carbs.
I have a 7044223 on the shelf that I decided to try. Its a holley "restored" carb so I was not planning on using it. Looks great but, as noted many times, the setup is all messed up. And it was.
The carb had UIAB in the air horn and in the body. The air horn IABs were plugged. The idle bypass in the body was plugged. The plugs were removed making the idle bypass functional. Other items that were suspect were a .169 idle bypass, a DCR at .063, MABs at .043, a LIAB at .052 (UIAB was .067).
First test with the stock 75 jet and 41 rod was very rich. In the high 9 - low 10 range. To be expected with a carb for a 454 on a 350. Next were 71 jets and then 69 jets with some improvements in cruze afrs (mid 11 to mid 12 afrs). The DCR was changed from .063 to .050. An improvement in the idle to off idle to the mid 12 to mid 13 ranges.
Still too rich. Started with changes to the IAB and MAB. Changes to the MAB were made (and tested) from .043 to .0465 to .052 to .063 and finally .067. LIAB changes (and tested) were .052 to .063 to .067. All air bleeds are now at .067.
The jets were changed to 67 and rods increased to 42. The secondary rods were change from DH to leaner AN. The secondary hanger was straighten to make them even.
After all of this, the carb has idle afrs in the 13.2 range. The off idle (1000 to 1300) afrs are in the high 13 low 14 range. Cruze (from 1300 to 2800) are in the high 13 to high 14 range. Light acceleration in the mid 14 to low 15 range. Heavy accelerationin high 11 to low 13 range.
Best of all were how stable the afrs are. Very consistent. The off idle afrs were right where I was trying to get to with the 7029207s. The idle afrs would fluctuate from 13.2 to 13.4. Not the random changes from low 13s to low 15s with the previous carb. Pickup has improved. Still need work on the secondaries.
Random thoughts, was concerned with the big idle bypass because they allowed the throttle to be almost closed. But it works fine. The 1974 choke mechanism sucks. The choke would come off way too quick (like as soon as the throttle was blimped). It was changed to a 1969 choke set up.
Its was 97 degrees today. The idle afr changed from 13.4 to 13.9 while sitting in traffic. The other carbs idle afr fluctuated form 13 to 15 in 70 degree weather.
Finally got a carb that works as it should.
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Do you have the APT system in the baseplate in play?
Holley "remanufactured" carbs are bottom of the barrel, they should never have been allowed to touch them. They clip off the post on the power piston and it needs to be there. If the post is clipped off the piston sits too deep so rods are deep in the jets and no way to fine tune part throttle A/F without taking the top off and changing parts.........
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Cliff, forgot to mention the power piston. Holley did cut the pin on the power piston. It was tossed and replaced with one that has the pin. I've collected several PP over the years. Most have the same height from the end of the pin to the top of the hanger. I used one of these.
I'll consider upgrading to an APT, but the last time I tried to remove the stock screw it would not come out. Buggered it up pretty good.
The Holley PP spring looked too long. It was replaced with one from a 7029207 carb. After all of the other changes were made, i'm seeing a sharp lean condition (afrs in the 17 range) at 1800 to 2000 rpm on wot. Power drops momentary then picks up. I suspect the PP spring is too weak. Would a weak PP spring cause the this condition.
Also not mentioned. Holley put inserts in the MABs and LIAB. The UIAB was not molested. I do not know what the air bleeds should be on the stock carb. So I was not concerned with drilling them to a larger size.
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APT is a nice feature on those units. Remove the cover, use some penetrating oil and heat from underneath with a propane torque. 99 percent of the time they will come right out. If you try to remove them before they are ready it usually results in breaking or mangling the screw.
I make a external APT screw with a spring on it so it holds it's adjustment.
Since you are tuning with a wide-ban you need this feature. Otherwise you are having to remove the top and change metering rods when all you had to do was keep the same metering rods and raise/lower it to get where you need to be.
In all the years I've been doing this I've found four defective castings. Two were 1971 Pontiac 7041262 Pontiac units. The other two were Edelbrock 1905 and a 1910. They had leaks between the main bowl and the passage under the DCR's.
I've rebuilt/restored hundreds of 7029207's and haven't ran into a defective one to date.
The lower IAB's are small and the uppers are larger for the originals and SR's. I've observed several different size idle tubes used in them and different jet/rod combinations. The originals that I've seen were a tad leaner for jets/rods on the primary side. I don't think any of them were altered prior to taking them in, but you never know with these things as they have been out there for half a century at this point......