Vacuum source on med riser 2X4?

[bmcmillan]

I have installed two Holleys on an Ford aluminum medium-riser dual- quad manifold.

Any ideas on where to get a vacuum source?

I could just drill into the plenum somewhere. There are a few undrilled/untapped blanks, but I don't know if they are vacuum, water, or mounting only.

Anybody know of a good Holley guy in Orange Co., CA area?

Brian

[Captain Speed]

My factory Ford 2x4 has the port at the rear.

[bmcmillan]

Speed,

Is it on the driver's side by the last runner or in the middle by the breather?

There is no hole there. It has what looks like was intended to be a mounting for something. Am I getting warm?

Brian

[SCOBRAC]

It's behind the rear carb facing the fire wall. Most likely you have a 3/8" nipple there now going to the brake booster. Install a 1/4 npt tee and put an 1/8 npt nipple on that.

[SCOBRAC]

What are your questions about Holley carbs. They are pretty easy to sort out with a little patience.

What are you running? What do you want to do. Aside from truing the faces of the metering plates and or carb body (which I suggest you let someone do with the proper machinery) there is little you can't do yourself.

[bmcmillan]

Michael,

Thanks a ton.

Mine isn't drilled and tapped. I'll do that this weekend.

Now I can have a 2x4 instead of a 2x2.

You made my day.

Brian

[Michael C Henry]

Vacuum source for what? Distributer vacuum advance or power brakes .What kind of a demand are you talking about. The vacuum to operate the secondaries is provided from under the carbs.

[bmcmillan]

Mike,

Any chance you could post a picture of your carb plumbing?

Now you know why I need a carburetor guy in socal.

Thanks,

Brian

[bmcmillan]

Mike,

Vacuum plumbing that is.

Brian

[SCOBRAC]

Brian,

Michael is right. Holley carbs pull secondary vacuum through the high pressure side of the venturi (within the carb) If yours are not opening you need a lighter spring.

What carbs are you using? Where they prepared for a dual quad engine specifically or are they "out of the box" 1850's or similar?

[SCOBRAC]

http://www.mortec.com/carbtip1.htm

[SCOBRAC]

I urge you to do get a book and get into these yourself. I know it will be way more trouble than it's worth but winter is coming and it will give you something to do. I know you live in So Cal but who wants to drive a Cobra in 70 degree weather in November and December anyway...

That said I reccomend two very talented carb shops, niether of which is in SoCal. Now obviously there are a ton of talented carb guys there and one I am aware of but have never used is:

Performance Carburetors
1408 South Grove
Ontario, CA 91761
(909) 673-1080

There are two here in Northern Calif.

JF Carburetion
2535 West Winton Ave.
Hayward, CA 94545
(510) 786-2505

Carburetor Factory
5757 Auburn Blvd.
Sacramento, CA 95841
(916) 339-3835

[bmcmillan]

Michael,

They are indeed 1850's. I realize that dual quads makes the engine way overcarbureted. They sure look cool though. I will take your advise and see if I can read up on them and make them work.

Thanks for the info.

Brian

[SCOBRAC]

Brian,

The carbs that came on a medium rise 427 were dual 715 cfm Holley 4160's. Your 600 cfm carbs are fine. What you need to first understand is that you will never come close to using 100% of their capacity of 1200 cfm. Just know you will only ever draw what your engine needs and no more.

Most FE's will draw 700-900 cfm. In the real world that means a 750 or 850 4150 double pumper or even a 4160 vacuum secondary 750. I run dual 450's for regular street use. They are 4160's but are mechanical secondary units.

Since you've decided to do this yourself know that anything you do wrong is easily fixed, nothing you can do to a Holley carb will damage your engine (aside from fire caused by sloppy work) and the worst you can do is learn something. Some things more than once.

The first thing you will need is a new set of vacuum secondary springs. You may want to start with the lightest springs and work your way up. You will notice a big difference in throttle response with a light verses a heavy spring, obviously whatever you do to one you need to do to both so be sure to get 2 of everything.

You know when you've gone too light with the springs when you get off idle,say 2200-2500 rpm and you are taking off fine and the engine suddenly bogs. If it doesn't actually bog but you get a belch of smoke you have also gone too far and may want to use the next heavier spring.

All 1850 Holley Carbs are equipped with a power enrichment circut called a Power Valve. Power Valves are like a shot of fuel controlled by the amount of vacuum in the low pressure side of the venturi. Once the intake vacuum drops to a predetermined value, in this case 8.5 inches (Hg) the valve opens.

Here's the thing, many mildly built FE's don't ever see 8.5" of vacuum. My 427 idles at 5.0-5.5" with the 450's. So you will first need to get a vacuum reading off the engine warm at idle. If the idle vacuum is over about 11.5-12" the standard power valves should be fine.

If your engine idles at 10" or less you will want to change the power valves to a lower number, generally 2.5-3.0" less than that of the normal idle value. I have 2.5's on my 450's

Assuming the carbs have not been molested, or significantly modified standard jetting will be fine for your 428. You can if you find at mid throttle you are belching fuel smoke or running rich rejet the 600's to something a bit leaner. You simply pull the rear (because your carbs are backwards) float bowl and remove the metering block and install new jets.

The 600's you are using are very close to the carbs Ford used in the 60's. Ford got over overcarburation issues in part by using a progressive linkage. That is the primary or front carb did most of the work, and depending on the way it was adjusted may have opened 30-50% before the second carb kicked in, often less.

I am from the school of whatever the front carb is doing the rear carb must also do. This is critical in a single plane performance manifold world or a multi carb setup. It isn't really important using a standard Ford dual quad manifold, nearly all of which were dual plane. This is part of the reason I opted for 450's. But I do the same with a pair of 660 cfm carbs I use from time to time. For drivability you may find adjusting the linkage to a given point for daily driving or cruising, and another point for better performance.

I don't have any photo's but I use to race a 12a Mazda rotary (1200cc) that employed a 1850 Holley. I was too poor or too stupid to realize they made a smaller carb. I'm sure the one I ran was free or nearly so from a swap meet. It drove and ran very well after a good deal of sorting.

Whatever you do only perform one task at a time, by that I mean don't go making two, three or four major changes off the bat. Start with taking a baseline vacuum reading. If the vacuum is in line with the stock power valves move on to another task. If not select a power valve and change them out, but don't make any further changes until you test run the engine. This will allow you you to undo anything you did without wondering what went wrong.

We'll be here to pick up the pieces if things get really bad. One thing you should always remember. Most "carb" problems are really fuel delivery problems. Stale fule, water in the fuel or dirt in the fuel or filter. One thing a Holley (or any) carb needs is clean fuel. If the idle circut air bleeds or the cruising circut air bleeds get dirty nothing will ever work right.

[SuperHart]

I Know someone who is running a pair of #8007 390 cfm Holleys on his dual quad 428FE and loves them. Crisp throttle response, great acceleration, and better fuel economy than with a single 750 cfm carb. I'm not sure what jets are being run but his secondary springs are one step lighter than stock. The secondary carb linkage is adjusted 1/4" behind the primary. Of course, they look identical to the 600s externally. He takes his manifold vacuum source off one of the PCV tubes on the carb baseplate and everything seems to work great.

[bmcmillan]

Michael,

Superhart makes a good case for dumping the 600's and getting 390's. You make a good case for trying to make the 600's work. I appreciate the help. I will see if I can get the 600's to work and if not, I'll get the 390's.

I'll keep you posted.

Brian

P.S. Today was a perfect Cobra day. 65 degrees and sunny. I just kept driving around in bigger and bigger circles.

[Michael C Henry]

I have the Dove tunnel wedge 2x4 intake. It's a single plane.I've made a port under the main plenium that connects the two carbs . Originaly I did it incase I had to incorperate a pvc. 1/4"npt and a brass elbow facing rearward with a short peice of blue silicone hose long enough to clear the carb bases. with the intake on and in the car you cat reach under the plenum withyour hand. At this point I have it hooked to a small vacuum storage tank inside the firewall .I was afaraid of pulsing vacuum with my cam for the Vintage Air heater and defroster ,as all Vintage Air products were vacuum controled. The carbs have the black secondary spring change covers for the secondaries.One cover has a hole the other cover has a peice of small tubing sticking out.I have an exagerated U of the same small tubing. One side of the U being longer than the other .The tubing connects the vacuum secondaries as a balance tube . The short end of the small U tube goes into the front carb vacuum secondary diaphram cover and the longer end connects to the short piece of tube byway of a small peice of vacuum hose. The longer side U tube lays on the choke cable housing anchor of the front carb as it goes to the rear carb That is all the vacuum plumbing my setup has .The distributer is centrifigual advance.

[Michael C Henry]

Watch if you have the 1850's or the like and the narrow perrimiter of the manifolds carb base flange.There are channels under the carbs base that are not seald off. The gasket is there but there is no manifold underneath to support the gasket and you end up with vacuum leaks. Guessford Machine filled parts of my carbs channels with JB weld(I think). My setup is hood clearence chalanged. So adding another plate and gasket is counter productive.
If I were doing this from scrarch and didn't have any induction, I'd go with a single four or EFI incorperated into a single four inake manifold , probably another tunnel wedge or a Victor open spider type.Not much available for dual fours.Nothing else is oem why should the carb be oem.They are making better stuff today.