Tuning Dual Quads

[oldimpala]

Hi all-

I've got a silly question... I've tuned my Edelbrock 1405 and 1406 a few times on my car (Usually after disassembly, and re-assembly for some reason), and I've always followed the same procedure:

1 Turn in on idle speed screws
1.5 turns on idle mix
Adjust linkage so they're operating "Evenly"
Fine-Tune the carbs identically
Check for Vacuum signal at manifold vacuum (w/ 2 Gauges) and set evenly as possible at idle


Is there any more fool-proof way to adjust, tune, and sync the carbs?

Another question is, does it really matter which carb has the choke (Front or Rear) with the stock linkage? I have mine in the rear, as "normal" for a 409, but a friend argued that there should be virtually no difference, and his arguments make sense on some levels..... I just put it there because it's where it was in 1963....

Could someone review their multi-carb tuning procedures with me? Especially if you've got a lot of experience with this stuff (Aubrey and the like), it's my first go with multiple carbs, and I just don't think I've got it quite right....

Any help here would be greatly appreciated, and maybe a good post in the Tech section (hint, hint...)

Thanks much-

-Andy/Oldimpala

 

[dq409]

Andy,,,Sounds good so far,,,,,
All I can say is throw those AFB`s in the corner and get the AVS`s !! heeee heeee
I also would like to know about about theory on the placement of the choke carb,,,dq

 

[oldimpala]

Carb tuning

DQ-

Actually, I'm thinking about going a different route... I just got off the phone (Literally) with Arizona Speed and Marine. I'm talking with them about doing a TPI setup for the '09.....

I'm just into doing things a little different; that's kinda why I built the w-motor in the first place.... Plus I know very little about FI, so it gives me the chance to learn.....


-Andy/Oldimpala

 

[Va348]

Oldimpala

Throw some ? out on FI,I play with these all my spare time.Have burn chip for the 730 ECM .I can help you to go the right places.

I am putting a all alu. LS1 in my 61 Bore & stroke to 409 you know. 4.035 bore 4 in stroke.

Have made a FI manifold out of a Tunnel Ram for a Nova.

Need any help just shout

Dale

 

[hotshoe]

is there a answer?

this is a old thread that could provide some good info that people like myself could use, but i think the real question here was never truly answered. does anyone have this knowledge they could pass along to rookies like me?
thanks,
kip

 

[Fathead Racing]

Quads?

I have a dual quad setup and 690's that will replace the three two 's/348 heads that are currently on my 62 .030 409. From my understanding the rear carb is the primary carb and will cruise on the front two barrels of that carb and will open the front carb when you stand on it, with progressive linkage. That means when you crank to start the engine you will open the rear carb (primary carb) primary throttle plates and depend on that (rear carb) accelerator pump shot to provide fuel for the start up. That means when you crack the primarys on that carb you will allow the choke plate to close. The secondary (front carb) would not come into play untill a preset position of the progressive linkage.The choke in this case would need to be in the rear (primary) carb. That's the way I have it set with my three two's. As far as setting the idle air bleeds, I would do just what Andy is doing using two vacuum gauges. My understanding when reading Andys post is that with stock linkage the front and rear primarys are opened as a pair, is that right? in that case it may not matter what carb the choke is on! For my money I like the progressive linkage. From a economical point it seems that running on two barrels instead of four would save fuel! For racing opening both carbs at once will be my choice.

 

[MRHP]

dual quads

Yes the rear carb is the primary carb on a stock progressive linkage. This is the reason the choke is in the rear. I just ran my 474 on a 180 mile trip with straight throttle linkage and got 13 mpg. I drove it easy most of the time, but I did run it up to 100 and did some burn outs with it too. So I guess the answer is yes you can have driveability and fuel economy with a straight linkage dual quad set up. Brian

 

[64ss409]

I think Ray and Brian have it covered. I just wanted to mention that the primaries of the rear carb are closer to the center of the intake, better distribution of air/fuel to the far cylinders. Thus the reason for the rear carb being the primary carb.
Ron

 

[mpris]

I noticed something on my 64ss/425. If while at idle I open the throttle on the front carb only, my engine seems to run very rough. If this is true on all of them, I would say that the fuel distribution is not real good from the front carb at least at low speeds. Maybe someone else could try this and see of their's acts this way. If its this way on all of them, I would say that the primaries of the front carb are too far forward in the intake to be used as for low speed application. Just a thought.

Poocho

 

[Ronnie Russell]

Well, its been a while since Ive been in trouble, but theres not much going on now so " why not?" I like direct linkage over progressive. Throttle response is much better and crisper Are you really only running on back primaries at 70 mph? I think if you checked gas pedal travel you would find you are using a lot more. It takes a "given" amount of fuel and air to maintain 70 mph. What differance does it make how you obtain that given amount? The progressive will get better milage over direct, but the improvment would be small. Now, for the choke. Those choke-tube type chokes never worked when they were new. A pain in the butt. 90% of 409 driving is in warm weather anyway. These are not EFI motors. You still gotta pump the pedal a few times to fire it up , then feather the pedal for a couple of mins. to warm her up. Whats wrong with that? I take the choke butterfly off and throw it away. Have never missed it. The exception would be the newer Carter or Edelbrock manual chokes which have a fast idle cam that actually works. But do you need it? Nah! You are gonna sit there and rev up the motor to warm it up because it sounds good. Its a w-head motor and the reason you own one is because its fun. You dont need a choke or a fast idle cam. It appears to me the front carb dumps on the upper level and then has to move to the rear to mix with lower level. Maybe this is why front carb is lethargic by itself. But this brings up an interesting fact. It takes 1 yr to 1 1/2 yr for a new manifold to go from drawing board to assembly line. The first 2 4bbl man. were first available in Sept. 61 so it must have been designed in early 60 or maybe even 59. Manifold designs have been improved drastically in the last 5 yrs. for most engines. Every year something better comes out and here we are using a manifold designed over 40 yrs ago. It just aint fair!! Can you imagine what Mr. Edelbrock could do for us if he wanted to? Its amazing our motors run so good with ancient technology. As far as tuning goes. the aforementioned method of using the vaccum gauge is as good as any. One caution for direct 2 4bbl linkage is it is important to check secondary throttle blade on front carb. Most of the time the secondaries come up short from opening all the way. This is easily fixed by shortening the travel by bending the little rod on the right side of the carb. that connects the primaries to the secondaries. You also need to make sure front carb. has a little effect on idle. The front carb. idle circuit is " in play" so it needs some fuel going through it at idle.Dont unscrew front idle screw thinking all of you idle quality is in rear carb. Gas prices are plummenting so hook them babies up direct and go have some fun.

 

[Skip FIx]

In the 70s my 409 Impala had two Holley 715s tunred sideways and the secondaries pinned to open(vacuum dashpot wouldn't fit), so all 8 opened directly. Was very streetable, but was a stick car. You could watch the gas gauge drop when all 8 were open full throttle! You could also tell the power was way down when the linakge fell off one carb.

 

[Skip FIx]

I tried to upload the picture but I get an error saying I've already posted the picture in a Mickey Thompson crossram thread, even when I rename the picture.

 

[JimKwiatkowski]

Re-use Photo

Skip,to re-use a photo,click on CP (control panel) then click on attachments,delete the photo from your attachment file,then you can post the photo in another thread.

 

[threeimpalas]

...These are not EFI motors. You still gotta pump the pedal a few times to fire it up , then feather the pedal for a couple of mins...

The W-engine would be a great candidate for an EFI setup. It'd benefit greatly from having the injector right in line with the runner, as witnessed by the performance of the mechanical FI setups used on these engines "back in the day".

The 3x2, progressively linked, 348 in the SDL doesn't need any pedal pumping or feathering on start-up; it starts like a charm each time. You need to get those carbs dialed in a little better.

 

[Skip FIx]

Ok here they are

 

[1958 impala]

duel fours

Oldimpala ,
Just a question about your 2X4S setup why did you run a 1405 and 1406 I just purchased two 1406s wondering if there is an advantage in runing a 1405 &1406

 

[jester]

OOOOH, OOOOOh, I know this one. One is elec. chock and the other manual. The manual choke carb is 2% richer and responds better. It is also cheeper. How did I do?

 

[Ronnie Russell]

Jester, Applause sign is now on.