They make tools for that.

Quadrajet Carb adjustment tool - Double D screwdriver? - CorvetteForum - Chevrolet Corvette Forum Discussion

C3 Tech/Performance - Quadrajet Carb adjustment tool - Double D screwdriver? - Does anyone have a good part number/ source for a Double D screwdriver that can adjust the Quadrajet carb fuel mixture screws? I have been searching for one, but for every It Works Great review, there are equal Didn't...

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The screw head is a double d.

 

Or look here.

Quadrajet Power, Your One Stop Quadrajet Shop

Quadrajet service, parts, kits, restored originals

quadrajetpower.com

 

This is the anti-tamper version that GM started using in the mid-70s for emissions reasons. You need the correct tool. I've had this one forever.

 

I ended up just cutting a notch in a random socket and that worked fine to twist the tuning screws, didn't really see any changes in vacuum when tuning though so I will have to look more into that.

 

Tools to turn Quadrajet double D mixture screws should be easy to find . The flexible ones are best to work with the angles you need. You can also order replacement mixture screws with a standard flat head slot .

 

Hello, I've been working on my project car for some time now, and have started to tackle issues with my sbc 350. For a long time I have had trouble starting the engine after recently running it. (for example stopping for gas). I fixed the choke and that made this issue better but not totally fixed. Now my biggest issue is the milage. I spent a night driving around town practicing manual driving for the first time, and noticed my gas being used up very fast. I ended the night with a calculated 5.2 mpg. This seams unrealisticaly low even for my setup. The carburator is a rochester quadrajet but it also has a edelbrock badge, not sure if that changes anything. I am doing all of this for the first time and could really appreciate some tips. I both want to be able to do it myself but also cannot afford the $300 quote for a "very basic tune up" from my many local shops. I have the timing set to 12 degrees BTDC. Please ask for any details I left out and thank you!

 

Could be a sunk float
post some pics of your carb.

 

I hope these are enough but I am willing to take it apart a bit if inside views would help.

 

I agree with needing to look at float. also what kind of fuel pump are you using? one off the engine or an electric?

also in the second to last photo under neither the air cleaner gasket, is the a hole? or is there a plug in it?

 

It is using the mechanical fuel pump from the engine. I can check the float but my only concern is would I need to get a gasket kit to reassemble it? I have a cruise planned this weekend and might want to wait for after that unless its something I can do in half a day.

I think this is the hole you were referring to, not sure what it is for but it does not have a plug.

 

That’s the access hole for the apt (adjustable part throttle).
If you’re going to drive it to the cruise just cover it with some duct tape for now. The fix involves carb tearing apart.
If it’s running rich then show us your spark plugs.
always a risk of tearing a gasket.

 

That’s the edelbrock version of the quadrajet. Same carb, just different name.
one more pic needed.
Warm it up to operating temp and at low idle take a pic of the top of the carb with the air cleaner off.

 

I will do this in a couple minutes just one question. I have an electric choke, do you want me to have it powered on for the picture? To be honest I still dont entirely understand the usage of the choke, I have it wired to a switch and just turn it on whenever I start the car so that it is open once the car is at operating temp, and leave it on for the rest of the drive. Is this the correct operation?

 

Thank you ill tape that hole

Here's a plug, need a expirenced opinion but it looks pretty dark to me considering it has less than 100 miles on it.

 

Yes. Have the power
on.

 

operating temp at 700 rpm idle :

 

Perfect. Choke is wide open.
A bit of of fuel on top of carb by the accelerator plunger could mean float level too high.
Plugs don’t look bad, Not black sooty anyway. Maybe a hard run up the autobahn would clean them up.

Look inside the carb while idling for any extra raw fuel. Shouldn’t be any.

 

dont see any extra fuel, I think my first step at this point should be a basic full rebuild, new gaskets and a couple of uprages I saw online. I suspect my tuning is also far off so I can get a fresh start to reset that after a rebuild. Thank you for your help!

 

Upgrades on line, eh!
Which ones?

 

bushing kit for primary shaft, epoxy bottom plugs (not sure if I would do that one), shorter accelerator pump (more volume). I am just regurgitating these from an episode of power nation as things I might as well do since I am taking it apart, if those aren't nessisary I won't do them.

 

I was thinking the same thing RW asked Online mods stop.

your best bet would be open it up you have some time to talk with RW and take some baby step’s.

you need to see what’s in there jet wise also more engine specs will help.

if you have a few bucks buy this book and read it. It will help you understand the workings of the QJet.

How to Rebuild & Modify Rochester Q Carb (S-a Design): Ruggles, Cliff: 9781932494181: Amazon.com: Books

How to Rebuild & Modify Rochester Q Carb (S-a Design) [Ruggles, Cliff] on Amazon.com. *FREE* shipping on qualifying offers. How to Rebuild & Modify Rochester Q Carb (S-a Design)

www.amazon.com

 

Bushing kit is a maybe. On a high mileage carb. Yours doesn’t look that used. In fact, I don’t think it’s been apart since new. The well plugs are for older carbs. They’re sealed better on the newer ones. You don’t need to mod the accelerator pump. You can adjust the linkage.
Buy a book like suggested.

 

Do you have a pic of the old spark plugs?

 

would this rebuild kit be all that I need? Edelbrock's kit also has one for 3x the price but I dont see many extra parts included.

 

I dont they were replaced when sold to me. I will get that book and go from there for sure. I do notice a couple small leaks around the carb so again a repair is definitely in need for now. I might hold off on the bushing unless I notice a lot of play. Thanks for the tips again.

 

That would work.
You’ll also need a torx bit or screwdriver for those star shaped screws.
And a tip if you pop the top off.
Don’t forget the two screws inside the Venturi near the boosters.

 

Get some books from the experts on QJets. Yes they are more complicated than just about any other carb but the fear factor far exceeds the reality.

How to Rebuild & Modify Quadrajet Carburetors – Cliffs High Performance Quadrajets

Rochester Carburetors & Emission Controls by Doug Roe; Bill Fisher: Good paperback (1973) | Orion Tech

Free Shipping - ISBN: 9780912656106 - paperback - HP Books - 1973 - Condition: Good - Rochester Carburetors & Emission Controls

www.abebooks.com

Bogie

 

You can get a book as suggested. But for me they are just a PITA problem child of carbs, exceptional when done right, but done wrong most of the time. Id put an AFB or a Holley on it and be done with it.

 

Also check ro see that the vacuum advance is working, since its primary purpose is to improve gas mileage at cruise speeds. If base timing 12 degrees BTDC, when you pull vacuum on the advance it should advance your timing about 18-20 degrees (about 30-32 total). If you don’t have a dial-back timing light to get a good measurement, at least verify that you get it to advance when vacuum is applied.

When there is no power to the electric choke it will move closed, so that when you start the truck (cold) you will have less air coming in, which gives you a richer mixture. The choke also move the linkage to a higher idle.
As the choke heats up from power being applied, it moves a curled bi-metallic strip inside and the choke gradually opens. Your original choke may have used engine heat to operate, , and the electric choke is a conversion. To simplify your operation and not require a separate switch, check for a wire to the wipers that only has power when the ignition is on, and use that for choke power.