7029241 Buick carb

[srb12]

Can someone give me the specifications for the carburetor of a 1969 Buick 430 engine with automatic transmission? Everything stock, except the air cleaner. 7029241.

Unfortunately I'm the owner of a commercially remanufactured unit which is no good right now. So I'm trying to get it right.

[Shiny]

Not sure what you are looking for but Cliff has a link to adjustment specs and there are old Delco part number summaries online.  If these will help and you need links, just ask.

[srb12]

Sorry for the late reply, I have a lot of trouble accessing this forum. Apparently my IP is banned and I have to access using my work's VPN.

I also reached out to quadrajetpower.com and according to them these would be the specs:

Idle tubes: .032
DCR: .047
Bypass air: none.
Low idle: .083
Upper idle: .052
Main air body: .058
Main air horn: .039

At some point I had:
Idle tubes: .035
DCR: .047
Bypass air: none.
Low idle: .083
Upper idle: .052
Main air body: .043
Main air horn: .043

I didn't ran very well, but later on I discovered I had ignition issues. But in the mean time I also had enlarged the main air body to .055 to be more close to stock.
However, today I found out that it runs worse when warm. Cold it fires right up, but as soon as the chokeplate closes it shuts off.
Quadrajetpower did say: "Smaller main bleeds will richen the mixture, which should be fine for todays fuels."

So I'm afraid I'm running really lean. On top of that, this post shows a difference between small block and big block idle mixture screws. Obviously I have the wrong ones, so I have to turn them way out.

https://www.corvetteforum.com/forums/c3-tech-performance/4248854-rebuilding-a-1969-rebuildable-core-quadrajet-carb.html#post1598998287

I know there is a lot of mixing and matching done with remanufacturing carbs, but after some online investigation I think I'm fairly lucky with regard to the baseplate, body and airhorn. The parts I have look identical to original 1969 carbs which sometimes are photographed on forums.
Obviously I'm a novice regarding Q-jets, so I'll probably miss stuff. But I have time to experiment some.
And living in Europe it isn't easy to find a good core, that stuff is rare here.

[Shiny]

Sounds like you have a good handle on it and got some good help.

I will follow your lead and verify my castings as I could also have a Frankencarb.  I'll also look at your link.

I have a 29240MD carb with a similar questionable pedigree and a bad performance history confused by other issues !!!!

So I'll watch for your updates.

I have been into my carb at least 3 times, with advice from Cliff and another knowledgeable carb guy on the PY Pontiac Forum.  My problem is a history of unstable idling and flooding.  I am currently replacing the gas tank to eliminate rust from the sending unit.  I am also going to address unstable timing by replacing disty springs/weights and the vibe damper.

My Buick carb is on a 350 Pontiac with a mild cam (Summit 2800) at 5800 ft. elevation.

Here are the last numbers I recorded.  They are different than yours so will be good to compare:

Upper Air Bleed      0.053
Down Channel      0.049
Lower Air Bleed      0.079
Bypass         0.089
Mixture Holes      0.090
Idle Tubes         0.035
Primary Jets           70
Primary Rods         44B
Secondary Rods          CH
Secondary Hanger         O
Power pump spring         6"  (Green or Black)

[srb12]

I thought I had my ignition problems left behind, but unfortunately it still isn't resolved.

So I'll address that first. I have my old Holley installed in the meantime to make sure the other issues have resolved before installing the Q-jet again.

I have it on the bench now and will make the main air bleeds smaller.
I'm not sure if I also have to enlarge the down channel restriction little bit to .051 for today's fuels:

"https://www.motortrend.com/how-to/quick-tech-ethanol-friendly-q-jet-rebuild/
"We accomplish this by measuring the idle tubes and increasing their size by .002- to .003-inch. We generally then like to see the channel restriction between .050 and .055 inch. Your mixture screws should then allow for proper mixture control."
My idle tubes are already a little bit bigger than stock, so this might be correct then.

I also just noticed that my air horn is little bit warped, so I have to correct that first. I'll look around on this forum for tips.

I don't think we should compare each others carburetor specs, yours is a small block and you're on altitude. No clue how that should affect yours.

[srb12]

Ignition problem resolved; it idles well now and I can kill it with the idle mixture screws.

Idle tubes: .035
DCR: .051
Bypass air: none.
Low idle: .083
Upper idle: .052
Main air body: .055
Main air horn: 0.43

Jets: .070
Rods: 44B
Secondary rods: AY.

Now I have to learn more about the carb.
Idling and part throttle are performing ok, but when I press the pedal deeper it holds back. I do see that the manual prescribes .045, so perhaps my 44B is wrong?
But I'm not experienced yet to tell if that has to do with the secondary system, or the primary or perhaps something else.

[Cliff Ruggles]

The B series rods for that carburetor all have .026" tips so at heavy/full throttle same metering with any particular jet being used......

[srb12]

I changed a few things on the secondary side. The hanger wasn't level, the airvalve spring was not wound up enough and I made a minor change on the throttle valve linkage.

Unfortunately I couldn't test it. It did start, ran very roughly for 15 seconds and then died on me. Tried to start it again, could get it to run for a few times, but very roughly and short only. Had the idea it was very rich. So I'm thinking the carb is leaking in the intake in the course a few days. I did test the well plugs, but only gravity feed with fuel. And I now see your method with soap, so will do that next.
 

[Kenth]

1969 and later Qjets rarely if ever have any problems with leaking bottom plugs.

Look for problems in the fuel inlet system, worn inlet needle & seat, old expired float, float setting etc.

[srb12]

Needle and seat are new from Cliff. Also passed pressure test.
I did revisit my choke settings and changed them a little bit, but I can see there is quite some fuel in the plenum. And I let it evaporate this afternoon and installed carb empty.
Choke plate is closed, vacuum break adjustment is 0.18 with diaphragm seated.
Fast idle is 3 turns after contact with cam.

Still think it's flooded. Sometimes seems to catch with choke unloader.

Strange. Had my choke on par, fired up immediately.

Checked spark once again, but thats fine. Initial is 8 degrees + manifold vacuum (which is per manual)

Edit: I have set my float height correct. Old float, how would I know? It was running well 2 days ago. Only with heavier throttle had some issues, but the secondary system had some faulty settings. But that doesn't do anything when idling/starting.

Have the carb now at WOT with a tie so everything can evaporate from the plenum.

[quadrajam]

Have you checked fuel pressure?

Also if you have a steel fuel line between your fuel pump
and carb make sure its not getting hot enough to boil
fuel in line. This will overcome any needle/seat/float
and spew fuel into the plenum.

[srb12]

Yes, 5 psi.
Latest part is rubber. But last times starting was the engine cold.

Strange is that it also started right away yesterday on the choke. Turned it right off, because I couldn't go for a drive. But was curious if it would start and it did.

[srb12]

Well it turned out I had a funky condenser. Worked sometimes, sometimes didn't. Multimeter tests aren't reliable apparently.

Fires right up on the choke. Idles well and stable, part throttle performs great and full throttle is fun Hot start is also great.

Thanks for your time Cliff! My remanufactured Q-jet luckily was salvageable.

Happy customer.

[Cliff Ruggles]

Good news!