[Half-Inch Stud]

See 12.2 ET Sig....my 9.0:1 470 needed the 1050 to idle, and certainly needed the Choke attached to thero-Spring to Start and Idle.

Any, all Q-JETs from 65-70 that i rebuilt would not start and idle. So i tried a pig-rich mod on the idle air bleeds and saw some improvement but the 1050 seemed better.

Solution:my 2 cents; more compression or less cam(dunno your specs), or maybe a 1972-1978 Q-JET has an improved chance of good start and idle on your 9.3:1. Oh, confer with CLIFF.

[srmmmm]

Originally Posted by Cliff R

First order of business is to strip it down and measure all the "players". Pressure/leak test the casting, verify no cross-leaking between the fuel bowl and area below the DCR's, throttle plates all FULLY closed'/tightly sealed in the bores when closed, no miss-matched components installed (different top/bottom), no lead plugs driving into bypass air holes, or any bleeds or orifices made larger or smaller than the stock size over the years.

In other words it's simply best in all cases, to pretend you know nothing about the carbs history and start from a clean slate. I'll also add here than more times than not you are a LOT further ahead to be working with a "virgin" unit vs one that's had a lot of hands on it as needed modifications will be simple and predictable.

.

Finally had the opportunity to tear down the carb and look for issues, but first, the history. I purchased the carb new in 1975 direct from Rochester Products. Up until this rebuild, the only things I ever did was to change jets and rods from those installed for a GS455 Stage-I to sizes that performed more effectively on my 350. Physical modifications were limited to polishing out casting lines and filling in linkage rod slots for more precise control of the choke plate. So I would consider this close to virgin, or maybe just a "First Base" date night unit.

The next event was the restoration work done which included new throttle shafts, an electric choke conversion, and rejetting for the 63 cu in displacement increase, 6X-4 head installation and use of a Comp XE276HR cam.

Upon disassembly, I noted the throttle plates all closed completely with no visible light showing around the edges and that the throttle shafts showed no play in the throttle body.

The float bowl did have some varnish/sludge in some crevices and the primary metering rods did seem to have some contact against the float bowl gasket. My concern was the appearance of the 2 brass idle air inlet restrictors. They seemed to be somewhat banged up, and I could not remember if there were originally 4 or just 2.

The four tubes in the air horn are not at the same height, one being about 3/16" shorter than the others. Pictures show these details. Considering the uniqueness of this unit, I certainly hope it is still usable.

[steve25]

The pickup tube that's driven in too deep is likely making the 4 cylinders that are feed fuel from that side of the Carb go lean at or around full throttle.

[Schurkey]

Originally Posted by srmmmm

Although a bit on the rich side, it ran very well on the dyno. Three years later (after covid interruptions), it's finally in the car and runs terrible. It starts fine and runs well as the choke pulls off on the fast idle cam, but refuses to idle when fully warmed up. I have to set the idle stop screw at the point where the engine is at 1500 rpm to run. It doesn't matter where the idle mixture screws are set. I can close them all the way or take them out all the way so the engine must be running on the main metering all the time.

The FIRST thing I'd do is to determine where the idle mixture screws are set now. Remove them. Grab a rubber-tip blow gun connected to compressed air, and blow into the threaded holes where the idle mixture screws were.

If you don't have compressed air, an aerosol can of carb cleaner with the red "straw" attached, could work.

This may blow any clogs of the idle passages back out the air bleeds.

Reinstall idle mixture screws to whatever position they were when you began. Start engine, see if you can adjust idle mixture screws and idle speed to something more reasonable.

This is the fastest, easiest, least-invasive potential fix. If this works, great. If not, move on to the more-intensive repair options.

[srmmmm]

Originally Posted by Schurkey

The FIRST thing I'd do is to determine where the idle mixture screws are set now. Remove them. Grab a rubber-tip blow gun connected to compressed air, and blow into the threaded holes where the idle mixture screws were.

If you don't have compressed air, an aerosol can of carb cleaner with the red "straw" attached, could work.

This may blow any clogs of the idle passages back out the air bleeds.

Reinstall idle mixture screws to whatever position they were when you began. Start engine, see if you can adjust idle mixture screws and idle speed to something more reasonable.

This is the fastest, easiest, least-invasive potential fix. If this works, great. If not, move on to the more-intensive repair options.

Extensive cleaning will begin tonight, but I had already removed the idle mix screws to verify they were the same tip profile and had the same spring lengths. Both were set at 1-1/2 turns open.

[Pav8427]

Thise idle tubes ARE mangled. The concern I would have is that someone opened the restriction way big.
The restriction is down at the bottom of the tubes and hardly measurable as installed. I wiuld pull them and check. Cliff has new ones and will drill them for you if need be.
Time to check all the proper dimensions and make sure someone didnt screw it up at some point.
Then get some new numbers for a recipe from Cliff.

[Pav8427]

Your carb also has the early base plate APT.
Cliff has a kit to change it to externaly adjustable.
That will help with the tine tuning once all is put back together.

[srmmmm]

Originally Posted by Pav8427

Thise idle tubes ARE mangled. The concern I would have is that someone opened the restriction way big.
The restriction is down at the bottom of the tubes and hardly measurable as installed. I wiuld pull them and check. Cliff has new ones and will drill them for you if need be.
Time to check all the proper dimensions and make sure someone didnt screw it up at some point.
Then get some new numbers for a recipe from Cliff.

Thanks for the observation. I was afraid of that. I would think the stock tubes would be fine considering the OEM application of the carb for a GSS455 Stage-I should handle my 413 cu in.

[srmmmm]

Finally had a chance to take in some of Cliff's experienced recommendations and did a careful reassembly of the carb. Three discoveries along the way: 1) wrong base gasket (left side of picture), 2) float height was set at 5/8" instead of 5/16", and 3) float pivot pin protruded above the level of the float bowl casting lifting the float bowl gasket and potentially binding the main metering rods.

It's back on the engine but waiting for daylight hours so I don't wake the neighbors when I start it.

[Kenth]

The previous history of this carb mean NOTHING. Obviously your carb is a hack-job from Quadrajet Power by looking at the pictures and what you´ve found by opening the carb. . You´ll have to measure the whole recipe and verify what you have NOW. Compare with factory specs and then make the proper modifications for your new engine.
I recommend getting Cliff´s book on Quadrajets for starters.

[steve25]

Something often overlooked in these carbs is the pivot hanger that the float hangs off of .

This needs to be bent such that sitting down the air horn to the body keeps this part held firmly in its notch.
If not then fuel pressure can un-seat the neddle and bounce the float around.

[Kenth]

Originally Posted by srmmmm

Finally had a chance to take in some of Cliff's experienced recommendations and did a careful reassembly of the carb. Three discoveries along the way: 1) wrong base gasket (left side of picture), 2) float height was set at 5/8" instead of 5/16", and 3) float pivot pin protruded above the level of the float bowl casting lifting the float bowl gasket and potentially binding the main metering rods.

It's back on the engine but waiting for daylight hours so I don't wake the neighbors when I start it.

1. Flange gasket to the left is correct for 1971 Buick units. Gasket to the right is for 1965-69 Chevy intakes which needs a steel shim on top of it.
2. Correct float setting for 7041242 is 13/32".
3. The slightly protruded float pivot pin is pushed down by the airhorn, with gasket in between, and holds the float in secure location. There is NO way it could cause binding of the primary metering rods.

7041242 uses #75 main jets with 45B primary rod, AV secondary rods and #7011957 power piston spring from factory.

FWIW

[srmmmm]

Originally Posted by Kenth

1. Flange gasket to the left is correct for 1971 Buick units. Gasket to the right is for 1965-69 Chevy intakes which needs a steel shim on top of it.
2. Correct float setting for 7041242 is 13/32".
3. The slightly protruded float pivot pin is pushed down by the airhorn, with gasket in between, and holds the float in secure location. There is NO way it could cause binding of the primary metering rods.

7041242 uses #75 main jets with 45B primary rod, AV secondary rods and #7011957 power piston spring from factory.

FWIW

Thanks for the observation on the float pin. I'll correct that condition. The jets, rods and hanger combo in the carb matches the Ram Air III which I though would be a better place to start at with my 413 ci displacement and XE276HR cam. I do have all the ones you mention though on hand.

[Pav8427]

Air bleeds and such were sized for the Buick application.
I presume that may change things a bit swapping over to Pontiac spec rods, jets and hanger.

[Kenth]

There is no way 1969 RA III jetting #72 jets with 41-42 rods or 1970 RA III jetting #70 jets with 39 rods will work in a 7041242, unless the main airbleeds are altered to Pontiac sizes and the brass nozzles in boosters are replaced with the larger and longer Pontiac nozzles.
You will also need to replace the power piston as the Pontiac rods are not aimed for the APT system used in the Buick carb. IF you do all the modifications for running RA III jetting you might as well cut the stop pin off at the bottom of power piston to make this work.
There is more but i`ll stop here.

If the airbleeds in your Buick carb are untouched you´d be better off using the original jetting instead of hackning your carb further.
The only thing your carb would have needed from the start are a couple or three of thousands of an inch larger idle tubes and some CV, AU or CK secondary rods then it will work like a charm.

FWIW

[srmmmm]

Originally Posted by Kenth

There is no way 1969 RA III jetting #72 jets with 41-42 rods or 1970 RA III jetting #70 jets with 39 rods will work in a 7041242, unless the main airbleeds are altered to Pontiac sizes and the brass nozzles in boosters are replaced with the larger and longer Pontiac nozzles.
You will also need to replace the power piston as the Pontiac rods are not aimed for the APT system used in the Buick carb. IF you do all the modifications for running RA III jetting you might as well cut the stop pin off at the bottom of power piston to make this work.
There is more but i`ll stop here.

If the airbleeds in your Buick carb are untouched you´d be better off using the original jetting instead of hackning your carb further.
The only thing your carb would have needed from the start are a couple or three of thousands of an inch larger idle tubes and some CV, AU or CK secondary rods then it will work like a charm.

FWIW

This is what is in the unit now which is what I had found listed in other postings for the Ram Air III. I'm not attesting to its complete accuracy, but the resulting metering area seemed appropriate:

74 jets with 45B rods
CH Secondary rods on an "I" hanger
Lightest power piston spring from Cliff.
Air valve spring at 3/4 turn initial tension.

Test run will be this evening.

[srmmmm]

Installed new 0.038 idle tubes and 0.055 down channel restrictors after thoroughly cleaning out all passages in the carb, carefully reassembled and put the correct base gasket on. Set the idle screws at an initial 3-1/2 turns and like magic, I've got an engine that will idle now!

https://www.youtube.com/watch?v=WEAOsbrju2U

I think I can still back off on the choke a bit as it seemed to stay on the fast idle cam longer than necessary, and I'm tempted to drop down one number on the primary jets to see if I'm still running on the rich side - an A/F meter is definitely on the wish list.

It was nice to be able to finally enjoy a Saturday night drive in "The Bird". Thanks to all the tips from members and the great forum thread history that provided the idle tube and restrictor sizing Cliff had recommended to someone with a similarly cammed 400.

[Pav8427]

Good news. Happy cruising.
Seems like we all like to tinker and learn from it.

[steve25]

Great to hear and thanks for reporting back.
Time to enjoy!