how do you set up 2x4 carbs

[saltshaker]

running a pair of 450's (9776's) on a 428.... whats the best way to dail them in? With the car in neutral if I punch the pedal they bog....has anyone set a pair of these up

Jon

[ERA Chas]

Jon,
Only way to help you is to suggest you search 'dual quads' and you will find 100's of posts packed with this info.
There's only about 10 or 20 things that will cause what you describe and many guys would first question whether it's your ignition and how you know.

[Mike Brasfield]

Bet it would be alot easier to use one large carb than 2X4.

[Barry_R]

This is personal opinion - and is gonna sound harsh - but I fix those carbs with a 1/2 inch wrench. They are mechanical secondary but without a rear accelerator pump. when I worked at Holley in the mid-80s-90s the engineering guys referred to those as "flamethrowers". They just open up too much throttle area without the necessary added fuel.

You'll be a LOT better off even with a couple of generic 600 vac secondary carbs.

[saltshaker]

the motor has 17 inchs of vacuum at idle with a comp 282s cam.....what power valves would you use. the carbs came with 8.5's
Jon

[Jerry Clayton]

I'm with Barry----those are the wrong carbs to be used on ANYTHING

[Excaliber]

First thing, gotta go with Barry on the carb selection, "flame throwers", that about sums it up.

Now, another BIG item to look for with bogging is base timing. Almost always it "aint enough". I can't recall exactly but I'm pretty sure my cam is also a 282S, solid flat tappet, lumpy idle, dual fours, idle speed below 1000 rpm is not the best, maybe 900 the least.

I've run THREE different versions of carbs on it and EVERYONE gave me a bog UNLESS, I set the base timing around 20 degrees! At that timing my starter is right on the edge of having hard time cranking the motor over when it's hot, so I back down the timing "just enough" to get the starter to work OK. That results in just a "slight bog", which WILL go away with just a bit more advance, but then starter issue...

SO, I bought a high dollar mini starter and the dang non-replacable strarter drive went out a year later. Couple hundred bucks down the drain. Went back to stock Ford starter ($50) and backed off the base timing "just enough".

Still here? It gets better. So then I bought a "Ready to Run" MSD distributor with vacuum advance, which for awhile I never hooked up. Base timing at 20, mech advance limited to 18, 38 total. More than I like, but it runs good and has about 7000 miles on it now. Some time back I started using the vacuum advance. WOW, really woke up the LOW RPM end of things! Without it I CANNOT drop below 2000-2100 rpm without the motor complaining. WITH IT, I can go down to around 1600 rpm and get smooth power flow.

I'm dialed in, and it wasn't the carbs. All though, in your case, it might well be that AND a timing issue.

At cruise rpm, around 3000-3200, with the vacuum advance I figure my total advance is 48. Base+mech+vacuum. I'm getting 11-12 mpg. 8.5 power valves.

EDIT: Just checked, I'm running the 292S, no doubt a little more aggessive than the 282? Could be why I need more timing than most?

[Bobcat]

To answer your specific question on the power valve .... divide the idle vacuum reading by 2 and add 1/2 to get a starting point for the power valve.
Looks like you`re close . X2 on the ignition . You can`t get the carbs right if the ignition isn`t correct . Again , X2 on as much initial advance as you can get away with ... and limit your max advance to 36 to 37 degrees . I have a Ponds 482 , single 4 bbl and run 26 degrees at idle and a max of 37 degrees with no run on or kickback .... BUT , every engine is different . I bought some different bushings for my MSD distributor that allow larger initial advance and yet limit the max to either 10 degrees or 14 degrees plus initial depending on the bushing selected . Learn to read your plugs ... they tell you what the engine wants/needs/has .
Again , ignition first , then carbs .

Bob

[saltshaker]

interesting thought: back a few months ago when I posted a question on which carbs to use the 450's were recommended more then any other carb. So I've been playing with them...power valves now 6.5's, jets #60's timing 16 int and 36 deg's total....runs a lot better and now idles. I'd like to see the difference
with a pair of bj/bk's ..............
Jon

[racco]

I have both carbs running at the same time (ford intake and 600 cfm vac) and no bog. I was told that one carb should run then the 2nd kick in, is this true?

[Excaliber]

Personally I disagree with that setup, some do it that way though. My carbs run equal throttle from idle to WOT. I think it give's better over all fuel distribution that way. I'd be concerned, perhaps wrongly, that staging the carbs would risk running the rear cylinders lean.

[racco]

I think they should work together also. I have never looked in the manifold to see if the passages are all linked together. All ferrari carbs (weber) work together, 6, 8 and 12 cylinders.

[Excaliber]

I'm pretty sure most all 2X4's manifolds are linked internally in some way to balance them front to rear. I know my original '64 intake does that. Never the less, I think there is still a danger of the rear cylinders running lean with only the front (or rear) carb in play.

[Lex]

1st off the 450's you have are mechanical secondary. Most 450's that people run are vacuum secondary. I have the same carbs. I run mine with progressive linkage. Whe the secondarys on the 1st carb start to open the primarys on the 2nd carb start. That gives you the shot of gas you need to get rid of the bog. Im still not proud of these carbs for street use. They were intended for a tunnel ram and drag racing where you come off the line at WOT. If I cant get mine dialed in right I'm gonna go with a set of 390 vacuum secondarys. As far as leaning out the rear cylinders, Im running a Blue Thunder intake and if you mount the carbs backwards the primarys on the 1st carb are right in the center of the engine. Of course this is an FE section and I'm running a small block in disguise.

[SuperHart]

Even though this subject has been discussed before here are a few ideas. Bog is usually caused by the throttle plates opening too quickly without a sufficient fuel shot causing a momentary super lean condition. When air flow through the secondary venturiis picks up enough to siphon fuel the condition disappears. This is why nearly all auto manufacturers go with vacuum secondary carbs rather than mechanical ones. With vacuum secondaries, the secondary throttle plates open gradually as engine demand increases. If you get a bog with a vacuum secondary carb when you nail the throttle Holley suggests installing a stiffer spring in the vacuum pot. That goes for dual quads also. With dual quads you must have a hose connection between the two vacuum pots to balance them.

Nearly all dual quad intake manifolds have runners connected to equalize and balance the vacuum and mixture signal to all cylinders. If the dual quads are reversed like on the Ford FE motors, the primary throttle bores of the primary carb are near the center of the motor and do give an adequately balanced mixture to all cylinders. Therefore, you can set up your linkage in a progressive manner so the secondary carb opens later than the primary one. Here again, crisper throttle response without the bog.

When setting the idle mix on a dual quad setup remember the rule of thumb for setting one carb, the idle mix screws turned out 1 1/2 turns from lightly seated. Now that you have TWO carbs, the settings are usually around 1/2 that for a single carb, i.e., turn the mix screws out 3/4 turn from seated on all four idle screws. The idle speed screws are also set the same way and are usually 1/2 the number of turns out. It does take some fiddling to get things right but the end result is worth the effort.

[Argess]

Originally Posted by SuperHart

Even though this subject has been discussed before here are a few ideas. Bog is usually caused by the throttle plates opening too quickly without a sufficient fuel shot causing a momentary super lean condition. When air flow through the secondary venturiis picks up enough to siphon fuel the condition disappears. This is why nearly all auto manufacturers go with vacuum secondary carbs rather than mechanical ones. With vacuum secondaries, the secondary throttle plates open gradually as engine demand increases. If you get a bog with a vacuum secondary carb when you nail the throttle Holley suggests installing a stiffer spring in the vacuum pot. That goes for dual quads also. With dual quads you must have a hose connection between the two vacuum pots to balance them.

Nearly all dual quad intake manifolds have runners connected to equalize and balance the vacuum and mixture signal to all cylinders. If the dual quads are reversed like on the Ford FE motors, the primary throttle bores of the primary carb are near the center of the motor and do give an adequately balanced mixture to all cylinders. Therefore, you can set up your linkage in a progressive manner so the secondary carb opens later than the primary one. Here again, crisper throttle response without the bog.

When setting the idle mix on a dual quad setup remember the rule of thumb for setting one carb, the idle mix screws turned out 1 1/2 turns from lightly seated. Now that you have TWO carbs, the settings are usually around 1/2 that for a single carb, i.e., turn the mix screws out 3/4 turn from seated on all four idle screws. The idle speed screws are also set the same way and are usually 1/2 the number of turns out. It does take some fiddling to get things right but the end result is worth the effort.

Good post. I run twin 600 cfm vacuum Holley's and except for one time when I had an internal carb leak, all plugs look the same indicating the same mixture. I do believe the front one primary being close to center does help.

The front carb opens approx 30% before the rear one but due to the linkage being more agressive on the rear, they both wind up at WOT at the same time.

I havn't found a need to have the transfer slot open at all. If I try for that, my idle is way too high even with the secondaries adjusted just shy of sticking.

I use the lightest vacuum springs avialable (but not the shorty ones) with no trouble.

And Superhart is right on with teh two carbs delivering twice as much fuel as required through the idle passage when at idle. I first used two generic carbs, and really couldn't get the idle to peak with the screws. ALl the way in seemed to be almost right. GUess some fuel must ahve been drawn through the transfer slots even though they wern't uncovered. Restricting the idle paassages in the primary metering block is the answer, and I had that done and wound up with all 4 screws about 3/4 turn out.

Now all that doesn't help if your carbs are mech secondaries. I would guess tghe recommendations to switch to vacuum units is not popular. Does this bog occur when you give it part throttle (primaries only open)? IS the bog gone if you give it WOT at higher rpms? If that is the case, it may be of note that I can only give my car 1/2 throttle in 2nd gear without fear of the losing traction. So you may be able to adjust your driving style for a while until you decide what to do.