Dual 94 carbs on a flatty setup questions

I already have headers and duals on my 47, and I picked up a dual carb edmunds manifold, and I have a lifetime supply of holley 94's around. Now eventually I'd like to get some aluminum heads, and definatly a hotter coil, it's already 12volt.

Anyway, does anyone have tips on where I can find info on seting up dual holleys? Like, what size jets to run, and what size power valve? I know there are different size power valves available for holleys. Anything else i should know?

 

Can't help on the power valves, but I got 51 for jets and it runs very well. Got stock heads and seems like a fairly stock cam. Tried smaller jets and it ran like s**t. Its a 255 53 Merc.

 

I`m running two bone stock work bench rebuilt 94`s on a two duece Fenton.
been running for about 10 years .
Just keep them clean

 

Thanks for the replies. That's good to hear, because I just had two of mine apart soaking in carb cleaner and both had #51 jets in them. I rebuilt the carb that is on it now, but that was a while ago and I don't remember the jet size in there, although I think that and one of the ones soaking are a matched pair.

 

The power valve size is very important. Alot of guys will plug them due to old articles written at the times when different sizes weren't available. 286merc is really the man to be answering this but since I haven't seen him around lately I will tell you that it depends on the engine setup but a good start would be a 7.5 power valve.

Carl, I hope you don't mind>

The KEY to using 94s by 286Merc



Lots of confusion still remains about using Holley 94's and vacuum only distributors on 8BA's and early Y blocks.
I'll just talk about the 1948-54 8BA style distributor.
Over 2 years ago I got into a discussion with an expert on another forum who positively stated that you could not run dual 94's and a stock distributor. When I said I better take my setup apart then all hell broke loose. A few others keep referring to an outdated 1954 magazine article like it was some type of gospel.

First of all there are over 17 varieties of the 94 style family, starting back in 1938 with the Chandler Grove and ending with the 1957 272 Y block for Ford production. Generic parts store replacements were available well into the 70's as the Holley 2100 and 2110. The Y block versions differ from the true 94 (which is the .094" venturi diameter) since they have a 1.0" and 1.062" venturi and often have a 1 or 1 1/16 marking on the side. There was even a 1 1/8" aftermarket version available that was quite common on hopped up VW's. The Lincoln V12 had a LZ casting which was also a 1" venturi. Bendix and Stromberg even got into the act, a Stromberg 94 clone actually has 97 on the side and is often found on EBay selling as a true 97!

The CFM of the 94 family varies from 150 to 190 for ones used on Ford vehicles. The larger venturies will give a slight power increase in even a stock or mildly modified engine.

Before attempting a tear down get a copy of the Ford procedure and a detailed parts blow up. It is part of the Shop Manual but some arent as detailed. The 1952 car manual or the aftermarket 1952-54 combined version is the best IMO.

I always suggest that users start with a matched pair of casting models that have the vacuum port on the lower right side of the bowl; you can not use the earlier versions without a vacuum port with the stock 8BA distributor. These carbs carry bowl ID's of 7RT, 8BA, 8RT, EAA, EAB, EBU, EBV, ECG, 2100, 2110 and probably some I missed. If you decide to use any of the Y block carbs then remove and plug the spark control valve in the base.

Another thing to check for is the nozzle bar, there were standard and hi-lift nozzle bars; dont mix types. The Shop Manuals suggested show the differences quite clearly. The drill bits specified for cleaning passages can be found at hobby/model shops. Guitar strings are good alternatives should they be handy.
After a thorough cleaning, check for any cracks, warpage or corrosion, repair or discard the bad piece. One old tried and true method of truing up the bowl and air horn surfaces is to place a clean sheet of 220 grit wet/dry paper on a pane of glass and gently slide the part over it; visually look for low spots. Finish off with 400 grit for a nice smooth surface. It is always good to have several parts carbs. Next step is to rebuild them exactly the same. Dont be suprised by what you will find inside of that flea market goodie, parts were often swapped without consideration of correctness even in carb shops. Just do both the same and to original specs.
Spend a little extra time polishing up any interior mold roughness; a Dremel works great for this.

Next is the throttle shaft. For dual carbs using drivers side linkage you need extended throttle rods. These can be found on many early and later carbs that used a hand throttle. Quite common on 1948 and later trucks as well.
Ford says .008" wear is OK but that usually also means the base casting is egg shaped by now and leaking vacuum like a sieve. The first step cure is an oversize shaft and a reamed base; try for a .002" fit. In extreme cases you will have to bore out the base and fit a bushing that should be a bit undersize and reamed to fit; getting everything realigned can get tricky. Several Internet and Hemmings advertisers can supply the needed parts or even rebuilt bases.

Then pay particular attention to fitting the butterflies to the throttle bores. That fit is VERY important and you might need to have several extra carbs (of any ID) on hand to find the tightest fit. The Y block plates are slightly larger than the flathead versions so dont get them mixed up. I like repeating myself about spare carbs.
Hold up to a light to check, there should be the tiniest sliver of light visible. Also be certain the bases arent severely pitted and butterflies corroded on the edges, a sure source of vacuum problems. ALSO be sure you dont reassemble the plates backwards!

Leave the choke plate in place for both carbs. Altho only one will be choked the plate is required for good air flow direction. Tests have shown a hp loss without the plate.

Next comes the true test, tuning them up.
I like to start with only one carb mounted with a known good air filter; not some restrictive import. Securely block off the other hole. Temporarily block off the vacuum line. Start the engine and adjust the carb for a good idle, be sure there are no vacuum leaks on this carb and over at the block off plate and at the manifold ports. Dishwashing liquid and water mix in a spray bottle works great. A leak sucking vacuum will cause a stumble, an air leak will cause bubbles. Do not ever use WD-40 or other flamable liquid. Warm up the engine and secure the choke wide open.

Now hook up a vacuum gauge to the carb port; dont even think about running duals (or trips) without one. Assuming the engine is tight, there should be around 18"/hg at idle. If it's much lower then it's time to trouble shoot. I'm assuming a non full race competition cam. Rev it up a bit, the vacuum should hold fairly steady thru at least 2500 rpm.
Note that Im leaving the distributor vacuum off for now and not worrying about the advance. If you are absolutely/positively sure the distributor is perfect then hook it up if it makes you happy. I personally prefer as few possible problem areas at this stage. Tweak the idle mixture screws for maximum vacuum and a smooth idle, actual rpm is not important but it is a lot quiter down around 5-600 rpm.

If everything is OK then swap carbs and repeat. Its a lot easier to get the idle set this way than with both in place plus you can find problems easier. And not place the blame on something else later on. If you havent installed the new intake yet then by all means do the initial adjustments on the stock one.

Now mount both carbs but no linkage. Get out the Uni-Syn that you should have bought along with the vacuum gauge. Use the Uni-Syn to measure/equalize air flow of both carbs AND the vacuum gauge to set final idle mixture. Final result should coincide with maximum vacuum. There are other balancing devices available, if you are familiar with their operation then use them.
Then hook up the linkage and do it all over again. This step assures that the linkage is not applying any control to the throttle rods. Tighten down the stops.
Be sure you pay attention to blocking off the not in use vacuum port. Only the front carb will be needed to provide a vacuum signal to the distributor.
By this time you should have 2 almost identical carbs.

Use clean, fresh and well filtered gas. If using an electric pump set the pressure regulator for 2.5 lbs maximum.

Hook up the choke cable to one carb, usually the rear. Hook up the vacuum line from the front carb to the distributor. Hook up the vacuum gauge to the rear carb; the original readings should be pretty close. If not check for hose or diaphram leaks.

Now its time for Truth or Consequences.
Extend the vacuum gauge hose into the vehicle. I prefer to have someone else do the reading while I pay attention to the driving. Record the readings throughout a full driving pattern, from idle to wide open throttle as you go thru the gears.
How does the response feel? Any pinging? Stumble or excessive loading/bogging down?

The ideal is to have the power valves open only when they are needed to enrich the mixture. This will be at or near full throttle or under a stiff load like going up a hill. Many of you may not ever want to wind things up that hard. The previous was intended more for stockers who are usually not going much beyond 2500 rpm. For rodders use the 2500 figure as a good place to start opening the valves.

If you are staying above 7-8" thru all phases of your way of driving then chances are you are good to go. Stock Ford power valves are 7.5's which means that at that vacuum they open. Tolerance is roughly 1 point either way.
If not then it will be necessary to go to a numerically lower power valve. This may raise a few eyebrows but try only one at first; the staggering effect may be to your liking. The front 2 cylinders are often starved with stock and some aftermarket intakes. Fuel flow is a hit and miss operation with all but the best designs.
In most cases a pair of 4.5's will handle all but the hairiest cam street engines. I run 4.5's on my 286 and 5.5's for many customer built 276's with Schneider .395" cams.
Go to the Holley Technical web site; power valves havent changed nor have the jets for almost 65 years; any speed shop can get what you need. Lots of good info on the Holley site. The new Holley "Hi Performance" PV's will work but require a bit of filing to clear.

The worse thing you can do is to plug or otherwise defeat the power valves in this configuration. Running 6 or 8 carbs on a hemi is something altogether different.

Once you're sure that the valves arent dumping too early then put in a fresh set of plugs and take a half hour ride at highway speeds. Read the plugs and change jet sizes ONLY if absolutely necessary. One size either way should be enough. Stock jets at sea level are .051; .049 and.047 were used at altitudes in the 5000-15000 foot range.
Sometimes changing to a different heat range or brand of plug is a better move. NKG BL6 plugs give me the best results and consistentcy. This is all called fine tuning.

So yes, dual 94's and a stock vacuum distributor are compatible a good many times. Dont expect to go racing or expect reliable fire beyond 4000 rpm; this is still a compromise since the distributor is not receiving the vacuum signal it was designed for. If you want a bit more advance (or reduced lack of as the distributor runs backwards from the typical vacuum operation) then turn the spring pins on the top of the plate with pliers. They are an eccentric and the spring tension is adjustable.
There are numerous conversions and aftermarket ignition options available; it just takes time and money.

The above was a compilation of over 45 years of using these carbs on flatheads and overheads, plus several articles in HRM and others going back as long, and finally some of the more recent books.
I would recommend Tex Smiths Flathead manual as good reading altho it is not without errors and omissions.
This article will also be useful in some areas when using 3 carbs, however there are differences involved. Thats another article for down the road.

 

Thanks! It sounds like I'm on the right track. I have at least two matched holleys that are in good shape, plus a bucket full of parts carbs. I have a '47 59AB engine, but it looks like most of the stuff carries over.

I'll be running the stock dual point set up on a dizzy machine and the '42 crab cap. I also plan on setting up each carb on the stock intake first.

Also, my dad was telling me the #51 jets would be much too big, and I should buy #46s. I think I'll try the 51's first and see what happens. I have my firewall mounted vacuum gauge that should come in handy!

I don't plan on racing around, I just want it to work good on the street going pretty easy on the old girl. I am a little worried my edmunds manifold with the carbs way back won't perform, but I'll try it.

 

I'm running a full house 49 merc with dual 94s. I set the carbs up originally like flathead J in cal. recommended. I bought his power valve plugs and 43 and 45 jets. It would hardly run. I finally got info from someone with my setup and he said use the stock power valves NAPA furnished in their rebuild kits and run 49 jets. Those power valves were 7.5. I rebuilt them again, I had that down pat by then, and all my problems were gone. Perfect off idle and all through the range. I was told, and it makes sense, that the fuel/air ratio must still be similar to stock whether one or two carbs which would mean close to stock jets.
Good luck, AV8 jon

 

Thanks for the input. My dad insists that although airflow will be cut in half buy two carbs, that the carbs will still want to deliver the same amount of fuel as if it were one carb. I think I'll try my 51's because I have them, if it runs way to rich I'll lean it out later. If not, I'll say I told you so, or better yet, let him think he was right

 

The airflow is what pulls the fuel into the carbs. The object of more carbs is more cubic feet per minute of air/fuel mixture to the engine. The fuel/air ratio therefore for optimum performance for a given engine should be close to if not the same. When you put two carbs on a stock or mild flatty you may think its running two rich when in fact its just too darn much air/fuel mixture. On a mild flatty I'd recommend an MSD box to fire the fouled plugs and also go 1 step hotter on the plugs.
Good luck, AV8jon

 

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My dad insists that although airflow will be cut in half buy two carbs, that the carbs will still want to deliver the same amount of fuel as if it were one carb.

[/ QUOTE ]

The fuel flow is controlled by vacuum created in the venturis of the carb. More air = more fuel. How much fuel the carb lets in is regulated by the jets. With two carbs, the airflow at the venturis will indeed be lower (not near half) & unless you change the jets, it will try to dump in more fuel - to a point.

It will be rich, but not nearly as bad as your dad thinks.

 

Thanks for all of these great tips. Now I'm working on a fairly stock 239, just headers and duals, so maybe I will want to jet it down a tad. Eventually I want aluminum heads, and I wanted a mallory until I heard it wouldn't clear the stock fan, so i'll probably set up my stock dual point on a dizzy machine and use a hot coil.

Any tips on hooking up the vacuum brake for the 59AB dizzy? I think it goes to manifold vacuum right now.

 

Just leave it hooked to manifold vac and be thankful you don't have a '49 with Loadomatic advance.

 

Oldie but goodie.

 

Wow throwback! I wound up doing an Isky max 1 cam and aluminum heads, and I put #43 jets in the Holleys and played a lot with the power valves, eventually settling on 3.5 in each carburetor. I ran it like that for years but it always had a little bog in it part throttle. A few years ago I rebuilt a pair of Stromberg 97's for it, I wish I had done it years ago, big improvement.