progressive dual quads.

Hi all,,

I just got the dual quad set up for my 350 (edelbrock), my question is when setting up in a progressive manner is it better to turn the idel mixure screws the same on bolth carbs, or is it better to set the rear carb as a primary and just use the front carbs idel mixture screws to ensure front cylinders are not running lean, So it would be 2 turns on rear screws 1/2 on front carb screws. i keep getting different answers when i call the manufactuer and i dont want to hurt the motor. Any suggestions?

With the AFB dual quads I had many moons ago, the front carb did not have idle screws, and the rear carb acted as the primary where you adjusted the idle. The front carb did not function until the progressive linkage activated it.

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Originally Posted by rumrumm

With the AFB dual quads I had many moons ago, the front carb did not have idle screws, and the rear carb acted as the primary where you adjusted the idle. The front carb did not function until the progressive linkage activated it.

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Rumrumm, do you think that helped the dual quad - cough, cough:LOL: - MPG?

That was back in 1969-71 when gas was 28 cents per gallon. Gas mileage? I didn't need no stinkin' gas mileage! LOL!

Dean, did you get your vacuum problem solved? Haven't heard back from you about it. Just curious why the thread of dual carbs when there was a problem to be solved. C'mon, inquiring minds want to know...:LOL::LOL::LOL:

almost. it was just running realy lean on the rear carb. Placed my hand on the carb to cover primaries and it smooth out a lot had slight stumble and the idel picked up, i adjusted the idel mix screws to 2 turns out on the rear carb and 1/2 on the front and it runs mutch better vacuum almost totaly steady 18 inches, but now i noticed one of the front squirters is dripping (hence the stumble ) but only when running, checked the floats and needle and seat , same thing, reduced fuel presure to 3 psi (just a test) and still dripping shut motor off and the drip stops instantly, fuel pressure does not drop stays where set. i have no idea, any suggestions?

P.S. thanks for all your help so far, you guys are great !!!!

Holleys or Edelbrock (carters)? Double check the check ball for the squirter. It should stop the drip. If not, you possibly have a gasket not seated in the right position between the body and top aloowing syphon backand creating a venturi effect. Holley's are slightly different because of design but same symptoms.

edelbrocks, where is the check ball ? do i have to remove the carb or just take of the top to get to it ?

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Originally Posted by Dean C.

edelbrocks, where is the check ball ? do i have to remove the carb or just take of the top to get to it ?

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It's underneath the primary squirters.

after 2 days of thrying to fix this problem, edelbrock told me to send them the carb they think somthing is cracked, we will se when i get thte new one how it runs.. thanks guys

Quote:

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Originally Posted by Dean C.

after 2 days of thrying to fix this problem, edelbrock told me to send them the carb they think somthing is cracked, we will se when i get thte new one how it runs.. thanks guys

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Just wondering if you ever got the 2x4 running, I would also like to ask this, is the 2x4 you are playing with on the air gap intake and which 4 is primary front or rear?

Hi all sorry i have not gotten back sooner small computer problem then i could not log back on,, anyways, i got the 2 4's working pretty good. very slight stumble at idel just needs a fine tune after motor breaks in. almost done i attached pics of car let me know what ya think.

Nice looking car!
I always like more than one carb! :3dSMILE:

Pat

Thanks, It is a 1936 plymouth 5 window
i have one question i just bouht a carb tuning dvd because they siad they showed how to tune 2 4's but it did not. so i e mailed the company on the dvd and asked them this is what they said.

I REALLY don't recommend running any kind of progressive linkage between the front and rear carbs on any twin carb set-up. Progressive linkage is great for six pack set ups where one CENTER carb runs the engine evenly up until half throttle, then the outer two carbs come-in later on (progressivly) for full throttle pulling.

Setting a front or a rear carb up as progressive can make the front or rear of the engine run lean, depending on which one comes in later. I would highly recommend running both carbs in perfect sync with each other.

Adjusting the idle mixture screws a bit more on the rich side for one of the carbs will only cause it to run slightly richer during, and right off an idle, but not at part throttle or while under normal acceleration. Under normal driving conditions, you are pulling from the main jets, NOT the idle mixture circuits that the screws adjust. They call them IDLE mixture screws for a reason :-)

Does progressive linkage work? Yes, but as I said.... IF there is a center carb to run the engine EVENLY, and 2 outer carbs that come-in progressivly as you get into the throttle. It is not good for your engine to have one carb running at part throttle while the other is closed. Make them both the same or you're asking for engine damage.

Have a good one,
Arron

Now i am nervuse i don't want to cause any damage to the motor, any suggestions?

Thanks Denny
this is the best pic i can get of the linkage, i'm just worries that i should be set up 1:1 insted of progressive.

yes that is the linkage i have. there instructions say it can be either way progressive or 1:1. depending on how you set it up. i have called there tech line numerus times and can never get a straight or the same answer on how to tune or set up, first it was 2 turns out on bolth, the next time it's 1/2 on front 1 1/2 on rear. then it was 3/4 turn on all. so i set it up 1/2 on front and 11/2 on rear progressive.
my problem now is i talked to a performance engine builder and he said never run progressive unless there is a center carb to even out the fuel or you will damage the motor due to a lean condition in the front (if the front is secondary) so now i dont know what to do.

ok, so for ideling i sould set all the idel mixture screws the same, and have the primary carb open a little before the secondary carb. If i do it that way witch carb should control the idel speed or should i use idel speed on bolth set at the same.

P.S. if i did not mention it before thanks for all your help..

OK, thanks again tommorow i'll try some different settings and i will let you know how i made out..thanks

Alot of things are needed to tune it, what type of build is the motor, stock, mild cam, street, race. I ran my cars 2x4's on a tunnel with progressive (not much), on the street, and on the boat with 1:1 with 2x4's on a blower.
I use a synchronizer ($15.-$25.00) and set them the same, 1st you need to set the carb Idle stop screws to what the book say's, you should not have to move them at all, if you do, don't go past the idle ports, or it won't idle right, and or hesitate. Then you start the motor and sync the carbs to the same vacuum, then turn your mixture screws evenly to set the idle, keeping the vacuums the same. once your there, you should be able to use either set up, you may have to back down your accelerator pump shots depending on you motor & or your jets. I don't know what jets you have, or need for your motor, but odds are you need smaller ones.
I adjust everything with the linkage off 1st, the I put it back on and make sure it still idles the same. After you get it tuned you can use the linkage both ways and see which you like best. You'll probably end up with 1:1

Pat

"....Alot of things are needed to tune it, what type of build is the motor, stock, mild cam, street, race....."

What Pat says is very true and some other things that need to be taken into consideration as well are vehicle weight, converter (if automatic), gears etc. Basically there is no one size fits all, each combination will react a little differently. On every dual quad setup I have run on my own stuff I have experimented with both synchronized and progressive to see what the car likes best. Some have liked one and some the other (and I have never hurt a motor by running progressive).

Denny has some good tips on the initial tuning set up. One thing I would like to add is to NOT be concerned when setting the idle that all the adjusting screws are turned exactly the same amount. Slight variances in the individual idle circuits and the way the fuel mixture flows thru the intake may require that one screw is adjusted a bit different than the other.

Basically every combination will be a little different and need various tweaks to get the most out of it. Don’t be afraid to experiment once it is dialed in you’ll love it.

Thanks guy's , the motor is

350, bored 40over.
edelbrock heads- 9.3:1 comp ratio with my pistons.
edelbrock cam Duration at 0.006" Lift: Intake: 278° Exhaust: 288°
Duration at 0.050" Lift: Intake: 204° Exhaust: 214°
Lift at Cam: Intake: 0.280" Exhaust: 0.295"
Lift at Valve: Intake: 0.420" Exhaust: 0.442"
Timing at 0.050" lift: Open Close
Intake: 5° ATDC 29° ABDC
Exhaust: 44° BBDC 10° BTDC
Lobe Separation - 112° Intake Centerline - 107°
metering rods have been changed (smaller) as per edelbrock.

I was just nurvouse , because i was told by edelbrock to run the rear carb at 1 1/2 turns and the front at 1/2turn (on idel mix screws) and now i'm hereing that could damage the motor because the front cylinders will be to lean.
so now i'm going to set it so bolth carbs are the same in the idle cuircut and runn a small amout of progresion like denny say's.

were can you get a carb sync tool for 4bbls iv'e seen them for 1 & 2 bbls?

Does your intake have a big plenum?

If so, seems the rear carbs primaries are very near the center and the A/F (Air/Fuel) mix should be fairly evenly distributed.

I don't see any problems with running progressive as long as it's a good product whether bought commercially or home-made.

I've seen the Edelbrock dual carb progressives on a couple of cars . . . nice product, well made, no complaints about throttle linkage from the guys who were using them.

If you're set up to do it, I'd make a progressive linkage my own self, something along the lines of what Edelbrock has done with two sliders on the linkage.

Be careful about progressive linkage, there's some real junk out there and some of it is potentially dangerous.
Couple years back I made a fuel log for an SBC in a well done 57 Chevy show truck running three 2 bbls.
The progressive on it was nothing more than bent wire.
Even the slider was a loop of bent wire.
Chrome plated - BFD - but it looked dangerous to me.
Commercially made by I don't know who.

That said, I like to run straight linkage on multi-carb setups.
The dual quads - 500 cfm Carters - on my 462" Buick ran great, 600 rpm idle with a fairly big cam, good tip-in on the secondaries which seemed to come in one after the other and not both at the same time.
Fun setup.

Here's some pics of the basic linkage, home-made with stainless steel and quality Heims.
Cost under $25. including the throttle rod to the gas pedal.

http://i49.photobucket.com/albums/f2...2DualQuads.jpg

http://i49.photobucket.com/albums/f2...ginemitfan.jpg

http://i49.photobucket.com/albums/f2...geDualQuad.jpg

Sorry about the linked pics.

They're from PhotoBucket and every once in a while on this site instead of showing the photo directly they end up like this.

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Since you'll be running with a reasonably light load on the engine when on the rear carb only, a lean mixture shouldn't hurt those cylinders.

At the horsepower levels most street driven cars run at, making a full 1/4 mile pass at the dragstrip with a slightly lean mixture doesn't seem to hurt anything.
Seen that done more than a few times.

i'm using the complete edelbrock set up, it's running pretty good now. i just did not want to hurt anything. i bought an air fuel monitor from edelbrock and put it in today tried a couple of different things today, it seemed to work best with bolth carbs on the idel cuirut almost even.

thanks for al your help guy's