two fours question

Background: 67 hi-po 289, bored .030, stock style pistons(less than 10:1), stock stroke, Pump gas-Pemium,Trick-Flo aluminum heads,MSD ignition,very aggressive camshaft(I can look up the specs if needed),Edelbrock aluminum intake with two Weber/Edelbrock 500cfm carbs. The step up springs in the carbs have both been changed to the weakest set due to aggressive camshaft and low vacuum at idle. The carb jets are factory at this time. Also use Holley electric fuel pump regulated to 7psi. The timing is at 14 degrees. Intake is gasket matched and it has big bore headers installed.

Problem: When idleing, for a short period, the enigne loads up and dies. The idle speed is 950-1000 RPM and the idle mixture screws are out one turn. The linkage is progressive and the chokes are open. If you rev the engine periodically to keep it cleaned out, it seems to help.

Question: Do I need to install smaller jets in the carbs? Do I need to lean the mixture screws some more? Higher idle? Any help would be appreciated. Thanks in advance  
1967 Fairlane 289-4v auto...for now
2007 Mustang
1997 HD F-250
2006 Taurus

I'm not real familiar with Edelbrock carbs, but they use metering rods with jets. you might have to change the rod to get the carb leaned out where it needs to be. Check this page of FAQs too: http://www.edelbrock.com/automotive_new/misc/tech_center/install/carb_faq.shtml

It states optimum fuel pressure should be 5.5 psi and no more than 6 psi, so you might be overpowering the floats and have raw fuel dripping in...

HTH...
Mark  
Mark Houlahan
Editor
Modified Mustangs & Fords Magazine

1965 FFR Roadster 427W/TKO-600
1966 Mustang 289-4V/C4
1968 Mustang 4.6L Three-Valve/5R55S auto
1990 Mustang 347/AOD
1998 Escort 2.0L SOHC/F4E-111 Auto
2002 Explorer Sport Trac 4.0L V-6/5R55 Auto

Often with the case of dual fours you have two idle mixture circuits to deal with and the volume is effectively double that supplied by a single four barrel. In that case generally you need to lean the system out. Remember that the idle screws do not affect the A/F ratio but instead act as a restriction orifice(semantics because it does affect what the engine ultimately sees). If you cannot lean out the mixture enough by turning the screws IN then you must reduce the size of the primary low speed jet.
This affect can be compounded with a fast idle because you can be flowing fuel in the transfer slot also as opposed to just the curb idle discharge ports. You will know this because turning your idle adjustment screws will have no affect on the idle. At Ford we often moved the transfer slot up(in the case of higher idle),,,, to keep it from flowing. Sometimes a quick fix is to use a file and extend the transfer slot on the UP side to reduce its tendency to flow, since it will bleed back vacuum depending on how  much slot is above the plates at idle.I dont recommend that on a carb body you want to keep since its chancy. We used carb bodies like paper cups, ya know use them once and learn then ,,throw em away. You dont have that option.  

I tried a dual four once with non-matching edelbrocks, but I didn't have a radical cam. Open question...isn't 1000 a bit high for idle? Have you checked for a vacuum leak? Have you checked float level? The edelbrocks I've played with are picky about float level if you ain't careful.Had to reset mine a couple of times due to lack of attention to instructions......I'm sure there is some good advice coming from other carb owners...want to hear myself, cause I got the matching carbs to put my 289 finaly..  

I set the idle to 950-1000 because it is a four speed car(65 fastback) and to try to improve the loading up. I've got some ideas from the folks who have replied to my post and I will try them Wed. She gonna get her first dyno run. Did I mention these are my last brand E carbs......  
1967 Fairlane 289-4v auto...for now
2007 Mustang
1997 HD F-250
2006 Taurus

Well I wouldnt necessarily blame the Carter/edelbrock carb. Its a good carb. Most of the name brands would have the same issues in dual fours. I have seen some where they block off the idle circuit entirely in one carb. They all come from the factory set at parameters that are for a normal stock engine. When you use those long duration cams, you get mixture dilution and  "over scavenging" which means at low speeds an unburned charge is drawn out a late closing exhaust valve. They can be very tricky to get to idle right, so dont feel like the lone ranger there. Most carbs use the same systems with just a little different way of doing it. I like the Ford 4100's, I think they are as simple a carb as you will ever find and very tuneable. I have never been a Holley guy only because you have to change the dang gaskets every time you do something and they tend to leak and have worse power valve problems then most carbs.  

If I were to block one set of idle circuits, should it be the front or the rear? Or is just a, see what my engine prefers, type of process. Thanks for the responses so far. And a side note this car has been to four car shows and brought home four 1st place trophies for its division with one best of show and one best engine of show. I'll try to post some pics.  
1967 Fairlane 289-4v auto...for now
2007 Mustang
1997 HD F-250
2006 Taurus

If the cam is real agressive, you may have too much idle opening.  What is your vaccum at idle and are you running vacuum advance?  Which carb has the PCV?  Ordinarily, you'd need to lean out the idle by increasing the size of the idle air bleeds.  On a 2x4, the rear carb is usually the primary so you could try closing down the front carb idle mix screws.  You have to make sure the primary throttle blades for the carb handling idle operations in not open into the transition area as that will pull excessive fuel due to the increased idle speed.  
1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.

As soon as I find the time I will look upthe cam specs. I am not running a vacuum advance or a pcv or brake booster on this engine. I will double check the amount of vacuum Wed. when she gets her first dyno run.  
1967 Fairlane 289-4v auto...for now
2007 Mustang
1997 HD F-250
2006 Taurus

> or a pcv

So how are you keeping negative pressure in the crank case?  
1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.

There is a breather on either valvecover, the owner did not want to look at a pcv valve and hose. I realize that is not the ideal setup. (That is not the only thing I would change.......)  
1967 Fairlane 289-4v auto...for now
2007 Mustang
1997 HD F-250
2006 Taurus

Tell 'em they are giving up power and it's make it that much harder to stabilize the idle.  Plus it'll shorten the life of the engine and require much more frequent oil changes.  Crankcase evacuation isn't there for looks.  
1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.

No doubt, on a show motor, a pcv is UGLY, but it IS necessary! Untold oil leaks will happen, and quickly. Some carbs have the pcv hose built into the front,some the back. If not are you running a spacer under the carb? Some of the older ford 4 bblspacers had those on the back. Some of those had a slight RAKE to them..shorter in the front, so when you accelerated, the bowls would be level..{in theory} thats what I heard...  

I have plead that case already, but he is confident that I can calm down the loading up without one.....  
1967 Fairlane 289-4v auto...for now
2007 Mustang
1997 HD F-250
2006 Taurus

Motors ran with draft tubes for years before we put in Positive crankcase ventilation. An open vented crankcase shouldnt cause any problems other then a little more air pollution. You only have a problem if its not vented then of course you can build up pressure to push out a gasket.