Anyone running 2 Holley 94's on thier flathead?

I’ve used jets between 47 and 52, depending on what’s bolted onto the engine. The jetting also depends on float settings and the rest of your setup. My linkage is straight 1:1, not progressive, for the intake I was using. I have a dual intake with Model 59 Holley 94 carburetors for it.

I’ve also used Carb Cheater. It creates a controlled vacuum leak to lean out the mixture when it’s running a bit rich. It has an AFR meter built into it, along with a tachometer, vacuum gauge, and voltmeter.

I’d 100% recommend an air/fuel ratio (AFR) gauge. It takes the guesswork out of figuring out whether you’re running rich or lean and makes tuning so much easier and less frustrating. You can see what’s happening while you’re driving instead of trying to read spark plugs and doing plug chops.

I also have a period-correct vacuum fan for the cab that I plan to install. It runs off a vacuum line, so turning it on for a breeze introduces some unmetered air into the intake. That could lean the mixture out a bit while cruising—something else I’ll be able to watch on the AFR gauge.
 
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Running one carb just uses the CFM of the one unit for function. With two or more units, the throttles can be progressive like a 4 barrel carb or their throttle movements can be halved to get the same response as with only one pair of venturis. Only one power valve would likely be needed. A lot of the given response depends on compression ratio, valve lift and other possible factors that change the engines needs. To dial in any fuel system, a person really needs an O2 sensor with an air fuel meter to read what is being consumed. That gives the ability to change the mixture to efficient flow rates. The ignition advance isn't as critical but it depends on how much the engine performance level has been changed.
 
Part of my mechanic job was I smog tech in CA. I also was going to say to weld a bung near the engine like a car with a 02 sensor has. Install a temporary fuel ratio gauge and sensor and dial the car in while you drive it around. Then you can screw a plug in the exhaust and use that new tool to dial in other cars. I haven't actually done this yet because I still healing from a stroke I had. I was going to dial in my flathead using one these tools, my '66 Shelby too, and many other projects I have.

Here is one guy's fuel ratio guage. It takes the guess work out of the fuel ratio so you can see what the fuel ratio is under all driving conditions. It's obviously not the only way to adjust carbs but it's the most precise. There are lots and lots of these O2 tuning videos, different types of gauges available. If you think this something you will be doing on this engine and other future projects, it might be worth the investment.

https://www.youtube.com/watch?v=2DYLhJ4hhx0
 
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I ran 2 94's for years with straight linkage only one of which had a power valve. Used what I think was called a "Uni-sync" to set them up. Worked great. Too long ago to remember PV size. Chap
 
A young fellow on you-tube developed the carb cheater system which basically uses an O2 sensor connected to a small control unit that bluetooths to any cell phone that's capable. It reads and tracks fuel usage in real time and has a manifold connection & MAP sensor where it can open or close it to compensate for a better fuel mixture ratio. It's simple and that's all it does but a person can make an old car run more efficiently and tune the carb for best overall efficiency. This explains it better than I can.
https://thecarbcheater.com/

It may not be practical for anyone that has an exhaust system that would not be compatible with O2 sensors and I don't know how reliable it would be but simpler is better when dealing with electronic components.
 
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chap52 said:
I ran 2 94's for years with straight linkage only one of which had a power valve. Used what I think was called a "Uni-sync" to set them up. Worked great. Too long ago to remember PV size. Chap
Click to expand...

Uni-sync is just for setting the idle openings of both carbs to make sure they are set exactly the same on both carbs at idle. So that both carbs are drawing in the exact amount of air at idle. Then you set the idle fuel mixtures by gently bottoming them out and then backing them out say around 1 1/2 turns. Now the "idle" is probably too rich, you turn the screws in a little bit until; the idle drops than back them out to the fastest idle, plus maybe a 1/8 extra. You go back and forth between two carbs trying to match the adjustment idle fuel mixture adjustment. Adjusting the other carb might change how the first one was running. When your done with both carbs' idle adjustment screws, they should be turned out the same amount. Both carbs are delivering exactly the same amount of fuel at idle. Then I stick the Uni-sync on them and make sure both idle openings are set the same, there both opened up exactly the same amount at idle. That's all a Un-sync does is make sure on multiple carbs the throttle blades are opened up identically at idle. Then I go back and double check it all again. When both carbs are evenly set then I hook the linkage up so that it doesn't move the carbs off of their idle stops and both carbs are open all the way when I step on the gas.

When I think I have the carb's "idle" adjusted perfect, I run a can of propane slightly opened over the top of the carbs and if the idle does not change the carbs are adjusted evenly. If the idle goes up the mixture is still too lean if the idle goes down the mixture is too rich, if it stays the same the carb or carbs is set perfect. Both carbs will have the mixture screws turned in or out exactly the same amount. The idle speed screws using the Uni-sync will be adjusted exactly the same. Now you have the idle mixtures and idle speeds of both carbs adjusted the same then you move on to setting the jets which controls the mixture off of the idle. The old way was to drive the car, pull the plugs and look at them to see if they are the normal tan or if they are black from being too rich. The new way is to install an air fuel mixture gauge and while you are driving it will tell exactly what your fuel mixture is and whether you need to make the jets larger or smaller. It's a really neat tool to own but one you won't use that often.

Then you also have the accelerator pump or pumps to try and adjust the spray of fuel while your carb or carbs switches from the idle circuit to the main circuit. There would be a momentary hesitation if it wasn't for that extra squirt of fuel. You have to find the right amount or fuel spray, so that it runs smooth through the transition otherwise it will momentarily bog down until the main circuit starts delivering fuel. Sometimes with multiple carbs the spray is too much, and you have to adjust the spray smaller.

It takes a lot of fiddling around with carbs to get them perfectly dialed in. It's not hard it just takes some experimenting.
 
Dad-gum fellers...y'all are giving this old guy an unexpected education. I guess I'm the simple type and you guys are the educated types.
The engine is a 1936, 21 stud, .060" overbore, Aluminum flywheel, 3/4 race cam, Fenton intake, Eddie Meyer heads, block hugger headers and the aforementioned 2 Holley 94's.
Thanks to you all...I have a lot of studying to do.
 
I installed dual 94s and an Edelbrock regular dual intake on the stock 239" in my '51 25 years ago that has resulted in good performance and trouble free driving. I used the wisdom from old time FB member 286 Merc on setting them up on a stock engine which included:


Use identical 94 model carbs. This is most important to ensure minimum setup and road performance issues.


Start with stock #51 jetting.


Drop the power valves from 7.5 to 6.5.


I use straight linkage, and a Uni-syn to adjust the linkage. I know some prefer (or think they want) progressive linkage, and that's your choice, but based on the problems some have had using progressive makes a good argument to at least start with straight, imo.


I initially used the stock loadomatic distributor that worked fine with the duals, but later switched to a NY Charlie-converted Chevy which provided a noticeable improvement, as many on here have also found. Earlier mechanical advance distributors will have no issues.


Bob
 
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